Iron powder coated with Mg-containing oxide film

ABSTRACT

Oxide-coated Fe powder for producing various electromagnetic circuit components requiring high resistivity is provided. The oxide-coated Fe powder is a Mg-containing oxide film-coated iron powder coated with an Mg—Fe—O ternary-based deposition film at least containing (Mg, Fe)O. The (Mg,Fe)O is a crystalline MgO-dissolving wustite. The Mg—Fe—O ternary-based oxide deposition film has a sulfur-enriched layer containing a higher concentration of sulfur than that of central portion of the iron powder, fine crystalline texture having a grain size of 200 nm or less, and the outermost surface is substantially composed of MgO. A composite soft magnetic material using the Mg-containing oxide film-coated iron powder is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the U.S. national phase application under 35 U.S.C. §371 ofInternational Patent Application No. PCT/JP2005/020204 filed Nov. 2,2005, and claims the benefit of Japanese Application Nos. 2005-016517filed Jan. 25, 2005, 2005-016516 filed Jan. 25, 2005, 2005-091053 filedMar. 28, 2005, 2005-122679 filed Apr. 20, 2005, 2005-155206 filed May27, 2005, 2005-155207 filed May 27, 2005, 2005-159770 filed May 31,2005, 2005-158893 filed May 31, 2005, 2005-158892 filed May 31, 2005,2005-161479 filed Jun. 1, 2005, 2005-161480 filed Jun. 1, 2005,2005-231191 filed Aug. 9, 2005, all of which are incorporated byreference herein.

TECHNICAL FIELD

The present invention relates to an iron powder coated with an oxidefilm containing MgO, having deposition films of Mg—Fe—O ternary-basedoxide formed on surfaces of iron powder particles, where at least (Mg,Fe)O is contained in the deposition films or ultra-fine particles ofmetallic iron are dispersed in the matrices of the deposition film, andto a deposition-film-coated iron powder for production of a compositesoft magnetic material having high resistance. The composite softmagnetic material made of the iron powder coated with the Mg-containingoxide film is used as a material for electromagnetic circuit componentsrequiring low core loss (iron loss), for example, variouselectromagnetic components such as motors, actuators, yokes, cores andreactors.

The present invention also relates to iron silicide powder coated withan oxide deposition film, having coatings of Mg—Si—Fe—O quaternary-basedoxide including Mg, Si, Fe and O on surfaces of the iron silicide powderparticles. The present invention also relates to a composite softmagnetic material made of a heat-treated compact (compacted powderarticle) of the coated iron silicide powder coated with an oxidedeposition film, to a core of various electromagnetic components made ofthe composite soft magnetic material, and to electric devices,especially reactors, equipped with the core.

The present invention also relates to an oxide deposition film-coatediron-based Fe—Si-based soft magnetic material powder formed by coatingoxide deposition films including Mg, Si, Fe and O on the surfaces of theiron-based Fe—Si-based soft magnetic material powder particles, and amethod of producing the same. Composite soft magnetic materialsmanufactured using the oxide deposition-film coated iron-basedFe—Si-based soft magnetic material powder are used as materials forabove-described various components of electromagnetic circuits requiringlow core loss.

The present invention also relates to composite soft magnetic powderformed by, on the surfaces of Mg-containing-iron-oxide-film-coated ironpowder which are formed by coating Mg—Fe—O ternary-based oxidedeposition films comprising at least (Mg,Fe)O on the surfaces of theiron powder particles, further coating MgO—SiO₂ composite oxide films(preferably forsterite having a MgO/SiO₂ value of 2 in molar ratio). Thepresent invention also relates to low core loss composite soft magneticmaterials manufactured using the composite soft magnetic powder andhaving high strength, high magnetic flux density, and high resistance.The low core loss composite soft magnetic materials having highstrength, high magnetic flux density, and high resistance can be used asmaterials for various components of electromagnetic circuits requiringlow core loss, for example, various electromagnetic components such asmotors, actuators, yokes, rotors, cores and reactors.

The present invention also relates to a composite soft magnetic powderformed by, on the surfaces of the Mg-containing-iron-oxide-film-coatediron powder which are formed by coating Mg—Fe—O ternary-based oxidedeposition films in which fine particles of metallic Fe are dispersed inthe matrix on the surfaces of the iron powder, further coating aMgO—SiO₂ composite oxide films (preferably composed of forsterite havingMgO/SiO₂ ratio of 2 in molar ratio). The present invention also relatesto low core loss composite soft magnetic materials manufactured usingthe composite soft magnetic powder and having high strength, highmagnetic flux density, and high resistance. The low core loss compositesoft magnetic materials having high strength, high magnetic fluxdensity, and high resistance can be used as materials for variouscomponents of electromagnetic circuits requiring low core loss, forexample, various electromagnetic circuit components such as magneticcores, cores of electric motors, cores of electric generators, solenoidcores, ignition cores, reactors, transformers, choke-coil cores, andcores of magnetic sensors.

BACKGROUND ART

Since low core loss is generally required for soft magnetic materialsused in various electromagnetic circuit components, it is generallyknown that hysteresis loss is reduced by reducing coercive force, andeddy current loss is reduced by increasing electric resistance.Moreover, because of recent requirements for down-sizing and highresponse of electromagnetic circuits, relatively high magnetic fluxdensity is considered to be important.

A Mg-containing oxide film-coated iron powder formed by coatingMg-containing ferrite films having insulating property on the surfacesof the iron powder particles is known as an example of theabove-described soft magnetic material having high resistivity (seePatent Reference 1).

A Mg-containing-chemical-conversion-film-coated powder formed by coatingthe Mg-containing-chemical-conversion-films on the surfaces of ironsilicide powder particles is known as another example (see PatentReference 2).

In addition, an iron-based Fe—Si-based soft magnetic powder containing0.1 to 10 weight % of Si, and the balance consisting of Fe andunavoidable impurities is known as another example. Soft magnetic powderformed by coating materials of high resistance on the surfaces of theiron-based Fe—Si-based soft magnetic powder particles is also known. Amanufacturing method of a composite soft magnetic material is known,where the soft magnetic material powder provided with the surfacecoating of high-resistance material is press-molded, and the obtainedcompact is heat-treated, thereby forming a composite soft magneticmaterial having high resistivity and a texture in which materials ofhigh resistance exist in interstices of soft magnetic particles (seePatent Reference 3).

In another known method, a Mg-containing iron oxide film-coated ironpowder coated with a Mg-containing ferrite film by a chemical process ismixed with glass powder having a low melting point to form a mixedpowder, the mixed powder is press-molded and heat-treated, and a compactpowder magnetic material is manufactured (see Patent References 4 or 5).

Patent Reference 1: Japanese Unexamined Patent Application, FirstPublication No. H11-1702.

Patent Reference 2: Japanese Unexamined Patent Application, FirstPublication No. 2003-142310.

Patent Reference 3: Japanese Unexamined Patent Application, FirstPublication No. H5-258934.

Patent Reference 4: Japanese Unexamined Patent Application, FirstPublication No. 2004-253787.

Patent Reference 5: Japanese Unexamined Patent Application, FirstPublication No. 2004-297036.

However, in the conventional Mg-containing oxide film-coated iron powdercoated with the Mg-containing ferrite film, the Mg-containing ferritefilm is coated on the surface of the iron powder through a chemicalprocess. Therefore, in the composite soft magnetic material obtained byperforming high-temperature heat treatment for reducing strain of apress-molded compact, the ferrite film is destabilized and changed, andits insulation property is deteriorated. In addition, bonding of theMg-containing ferrite film to the surface of the iron powder is notsufficient, and a composite soft magnetic material having sufficientstrength cannot be manufactured by press molding and subsequently bakingthe Mg-containing iron oxide film-coated iron powder. In composite softmagnetic materials manufactured by press molding and baking theMg-containing oxide film-coated iron powder coated with the conventionalMg-containing ferrite film or by press molding and heat treating themixed powder obtained by mixing the glass powder having a low meltingpoint with the Mg-containing iron oxide film-coated iron powder coatedwith the Mg-containing ferrite film, the Mg-containing ferrite filmcannot exert a sufficient insulation effect because of delaminationduring the press molding or the like, and therefore sufficient hightemperature resistivity cannot be obtained.

In addition, in the chemical-conversion-film-coated iron silicide powdercoated with the conventional Mg-containing chemical conversion film,since the Mg-containing chemical conversion film is coated by a chemicalprocess, bonding strength of the oxide film to the iron silicide powderparticle is weak and the oxide film itself has weak strength. Therefore,in the complex soft magnetic material manufactured by press molding andbaking the conventional chemical conversion film-coated iron silicidepowder, the chemical conversion film cannot exert a sufficientinsulation effect because of delamination or tearing of the film duringthe press molding or the like, and therefore sufficient high temperatureresistivity cannot be obtained. In addition, the chemical conversionfilm formed by coating the above-described Mg-containing chemicalconversion film by a chemical process is sometimes degraded during thehigh temperature baking treatment for removal of strain, therebyreducing the resistance, and therefore, a complex soft magnetic materialhaving sufficient high temperature resistivity cannot be obtained.

An Mg-containing ferrite oxide film may be considered as an example ofhigh resistance material formed on the particle surface of theabove-described iron-based Fe—Si-based soft magnetic powder. However,even when an iron-based Fe—Si-based soft magnetic powder coated with theMg-containing ferrite oxide film is press-molded into a compact, andstrain-relief heat treatment at a high temperature is performed on thecompact, sufficient high-temperature resistivity cannot be obtained.Because the Mg-containing ferrite is generally unstable in relation toheat, its insulation property is easily reduced by the change of ferritestructure caused by heating. As a result, insulation property of theobtained composite soft magnetic material is reduced.

In addition, in the iron-based Fe—Si-based soft magnetic powder coatedwith the conventional Mg-containing ferrite oxide film, theMg-containing ferrite oxide film is coated on the surface of powderparticle through a chemical process. Therefore, bonding of theMg-containing ferrite oxide film to the surface of iron-basedFe—Si-based soft magnetic powder particle is not sufficient. Therefore,in the composite soft magnetic material manufactured by press moldingand heat-treating the iron-based soft magnetic powder coated with theconventional Mg-containing ferrite oxide film, delamination or breakdownof the Mg-containing ferrite oxide film or the like occur during pressmolding, and sufficient insulation effect cannot be exerted. Therefore,sufficient high resistivity could not be obtained.

DISCLOSURE OF THE INVENTION

The inventors performed research to manufacture a Mg-containing oxidefilm-coated iron powder having such properties that: the oxide film isfirmly bonded to the surface of iron powder particle, and when thepowder is press-molded, breakdown of a high resistance oxide film on thesurface of the iron powder particle does not occur during the pressmolding; when strain-relief heat treatment at a high temperature isperformed after press molding, surface insulation is not reduced, andthe powder has high resistance, low eddy current loss; and a coerciveforce can be further reduced and hysteresis loss can be further reducedin the case of performing heat treatment of the powder for straighteningannealing.

As a result, the below-described findings could be obtained. Firstly,iron powder (hereafter referred to as oxidation-treated iron powder)having a surface coating of iron oxide is formed by heating an ironpowder in an oxidizing atmosphere.

The oxidation-treated iron powder is mixed with an Mg powder, and theobtained mixed powder is subjected to heating or the like in an inertgas atmosphere or in a vacuum atmosphere. After that, a secondoxidization treatment is performed on the powder.

The following are the findings with respect to this powder.

(A) MgO—FeO—Fe₂O₃ ternary-based oxide is represented by, for example,(Mg,Fe)O and (Mg,Fe)₃O₄. Among this generally known Mg—Fe—Oternary-based oxide, at least (Mg,Fe)O is contained in Mg—Fe—Oternary-based oxide deposition films formed on the surfaces of ironparticles. The Mg-containing oxide film-coated iron powder having asurface coating of the Mg—Fe—O ternary-based oxide deposition filmcontaining at least (Mg,Fe)O is remarkably superior in bonding of theoxide film to the iron powder compared with the conventionalMg-containing oxide film-coated iron powder formed by coating anMg-containing ferrite on the particle surface of iron powder. Therefore,there is a lesser possibility that the oxide film as an insulation filmis broken down during the press molding and particles of the iron powderare made to contact with each other. Therefore, when the press-moldedpowder is subjected to strain-relief heat treatment (heat treatment forreducing strain) at a high temperature, high resistance is maintainedwithout reducing the insulation property of the oxide film. Therefore,eddy current loss is lowered. In addition, since the coercive force canbe further reduced by the strain-relief heat treatment, hysteresis losscan be reduced to a lower level. Therefore, a composite soft magneticmaterial of low core loss can be obtained.(B) It is preferable that the (Mg, Fe)O contained in the Mg—Fe—Oternary-based oxide deposition film of the above-describedMg-containing-oxide-film-coated iron powder be a crystallineMgO-dissolving wustite (a solid solution of MgO and wustite (FeO)).(C) A sulfur-enriched layer is formed in a boundary portion between theiron particle and the Mg—Fe—O ternary-based oxide deposition film atleast containing (Mg,Fe)O. Sulfur concentration of the sulfur-enrichedlayer is higher than that of sulfur contained in a central portion ofthe iron particle as an unavoidable impurity.(D) The above-described Mg—Fe—O ternary-based oxide deposition film atleast containing (Mg, Fe)O has a fine crystalline texture having a grainsize of 200 nm or less.(E) It is preferable that an outer-most surface of the above-describedMg—Fe—O ternary-based oxide deposition film at least containing (Mg,Fe)O contain as much MgO as possible. Most preferably, the outermostsurface is substantially composed of MgO.

The present invention is made based on the above-described findings andhas the following aspects.

(1) A Mg-containing oxide film-coated iron powder comprising iron powderparticles and Mg—Fe—O ternary-based oxide deposition films which containat least (Mg,Fe)O and are coated on surfaces of the iron powderparticles.

(2) A Mg-containing-oxide-film-coated iron powder as described in theabove-described (1), wherein the (Mg,Fe)O contained in the Mg—Fe—Oternary-based oxide deposition films of the Mg-containing oxidefilm-coated iron powder is a crystalline MgO-dissolving wustite phase.(3) A Mg-containing-oxide-film-coated iron powder as described in theabove-described (1) or (2), further comprising sulfur-enriched layers inboundary portions between the iron powder particles and the Mg—Fe—Oternary-based oxide deposition films at least containing (Mg,Fe)O,wherein sulfur concentrations of the sulfur-enriched layers are higherthan that of sulfur contained as an unavoidable impurity in centralportions of the iron powder particles.(4) A Mg-containing-oxide-film-coated iron powder as described in theabove-described (1), (2) or (3), wherein the Mg—Fe—O ternary-based oxidedeposition films at least containing (Mg,Fe)O have microcrystallinestructures having a grain size of 200 nm or less.(5) A Mg-containing-oxide-film-coated iron powder as described in theabove-described (1), (2), (3) or (4), wherein outermost surfaces of theMg—Fe—O ternary-based oxide deposition films at least containing(Mg,Fe)O are substantially composed of MgO.

As described above, the Mg-containing-oxide-film-coated iron powder ofthe present invention as described in (1) to (4) can be produced by:firstly producing an oxidation-treated iron powder by forming iron oxidefilms on the surfaces of iron powder particles by heating the ironpowder in an oxidizing atmosphere, performing heating or the like in aninert gas atmosphere or in a vacuum atmosphere on the mixed powderobtained by mixing the oxidizing-treated iron powder with a Mg powder,and further performing a second oxidizing treatment to heat the mixedpowder in an oxidizing atmosphere. More specifically, theMg-containing-oxide-film-coated iron powder of the present invention maybe produced by: firstly producing an oxidation-treated iron powder byforming iron oxide films on the surfaces of iron powder particles byheating the iron powder at a temperature of 50 to 500° C. in anoxidizing atmosphere, heating the mixed powder obtained by mixing theoxidizing-treated iron powder with a Mg powder at a temperature of 150to 1100° C. in an inert atmosphere having a gas pressure of 1×10⁻¹² to1×10⁻¹ MPa or in a vacuum atmosphere, and further performing a secondoxidation treatment to heat the mixed powder at a temperature of 50 to350° C. in an oxidizing atmosphere.

The Mg—Fe—O ternary-based oxide deposition films containing aMgO-dissolving wustite phase and having an outermost surfacesubstantially composed of MgO as described in the above-described (5)may be produced by: firstly producing oxidation-treated iron powder byforming iron oxide films on the surfaces of iron powder particles byheating the iron powder at a temperature of 50 to 500° C. in anoxidizing atmosphere, heating the mixed powder obtained by mixing theoxidation-treated iron powder with a Mg powder of a further large amountat a temperature of 150 to 1100° C. in an inert atmosphere having a gaspressure of 1×10⁻¹² to 1×10⁻¹ MPa or in a vacuum atmosphere, and furtherperforming a second oxidizing treatment to heat the mixed powder for afurther long duration in an oxidizing atmosphere.

The Mg—Fe—O ternary-based oxide deposition films formed on the surfacesof iron powder particles of the present invention contain at least(Mg,Fe)O. It is more preferable that the (Mg, Fe)O contained in theMg—Fe—O ternary-based oxide film be a crystalline MgO-dissolvingwustite. Most preferably, the outermost surface of the deposition filmat least containing (Mg, Fe)O may be composed of MgO. Content of oxygenin (Mg,Fe)O is not limited by the ratio of (Mg,Fe):O=1:1, but may have arange of solubility.

In general, the term “deposition film” indicates a film formed bydepositing vacuum-evaporated or sputtered film-forming atoms, forexample, on a substrate. In the present invention, the Mg—Fe—Oternary-based oxide deposition film at least containing (Mg, Fe)O andformed on the surface of iron powder denotes a film deposited on thesurface of the particles of iron powder being accompanied by reaction ofMg and iron oxide (Fe—O) on the particle surface of theoxidation-treated iron powder. The Mg—Fe—O ternary-based oxidedeposition film at least containing (Mg, Fe)O and formed on the surfaceof iron powder preferably has a film thickness in a range from 5 nm to500 nm so as to ensure a high magnetic flux density and high resistivityof a composite soft magnetic material formed by compacting the powder.Where the film thickness is smaller than 5 nm, it is not preferable,because the composite soft magnetic material formed by compacting thepowder cannot have a sufficient resistivity and has an increased eddycurrent loss. On the other hand, where the film thickness is larger than500 nm, it is not preferable because the composite soft magneticmaterial formed by compacting the powder has a decreased magnetic fluxdensity. More preferably, the film thickness may be in a range from 5 nmto 200 nm.

The Mg—Fe—O ternary-based oxide film at least containing (Mg, Fe)O as aconstituent of the Mg-containing-oxide-film-coated iron powder of thepresent invention has a sulfur-enriched layer at the boundary portionbetween the Mg—Fe—O ternary-based oxide film at least containing (Mg,Fe)O and the iron powder particle, where the sulfur concentration of thesulfur-enriched layer is higher than that of sulfur contained in thecentral portion of the iron powder particle. The presence of thesulfur-enriched layer may be confirmed by an analysis of the sulfurconcentration by Auger electron spectroscopy, where a peak of the sulfurconcentration is shown in the graph. By the presence of such asulfur-enriched layer at the boundary portion, the Mg—Fe—O ternary-basedoxide film at least containing (Mg, Fe)O has further improved bonding tothe surface of iron powder particle, breakdown of the deposition film isprevented by tracking of the deposition film to deformation of thepowder at the time of press-molding the powder, high resistance ismaintained by preventing contact and bonding of iron powder particleswith each other at the time of heat treatment, and therefore eddycurrent loss is reduced. The iron powder contains sulfur as unavoidableimpurities. It is considered that most of the sulfur in thesulfur-enriched layer is provided by the sulfur contained in the surfaceportion of the iron powder.

It is preferable that the grain size of crystals constituting theMg—Fe—O ternary-based oxide deposition film at least containing (Mg,Fe)O and formed on the surface of the iron powder particle of thepresent invention be as small as possible. Preferably, the depositionfilm has a fine crystalline texture having a grain size of 200 nm orless. Because the fine crystalline Mg—Fe—O ternary-based oxidedeposition film has such a fine crystalline texture, the deposition filmtracks the deformation of powder particle during formation of thecompact, and is prevented from breakdown. At the time of heat treatment,the iron powder particles are prevented from contacting and bonding witheach other. When the powder is subjected to strain-relief heat treatmentat a high temperature, because of the stable property of the oxide,reduction of insulation is prevented, and eddy current loss is lowered.Where the grain size is larger than 200 nm, it is not preferable,because the film thickness of the Mg—Fe—O ternary-based oxide depositionfilm exceeds 500 nm, and magnetic flux density of compacted compositesoft magnetic material is reduced.

The MgO content in the outermost surface of the Mg—Fe—O ternary-basedoxide deposition film at least containing (Mg, Fe)O and constituting theMg-containing oxide film-coated iron powder of the present invention ispreferably as high as possible. It is most preferable that the outermostsurface be substantially composed of MgO. Where the outermost surface issubstantially MgO, diffusion of Fe is inhibited at the time of heattreatment of the press-molded compact, the iron powder particles areprevented from contacting and bonding with each other, reduction ofinsulation is prevented, high resistance is ensured, and eddy currentloss is lowered.

The above-described Mg—Fe—O ternary-based oxide deposition film at leastcontaining (Mg,Fe)O and constituting the Mg-containing oxide-film coatediron powder of the present invention may be a pseudo ternary oxide filmin which 10% or less of Mg is replaced by one or more elements selectedfrom Al, Si, Ni, Mn, Cu, and Co.

In the Mg-containing oxide film-coated iron powder of the presentinvention, it is preferable to use the powder having a mean grain sizein a range from 5 to 500 μm. The reason for this limitation is explainedas follows. Where the mean grain size is smaller than 5 μm, it is notpreferable, because the compressibility of the powder is lowered andvolume fraction of the powder is decreased, and therefore the value ofmagnetic flux density is lowered. On the other hand, where the meangrain size is larger than 500 μm, eddy current in the powder isincreased, and magnetic permeability at high frequency is reduced.

Next, a method of producing a composite soft magnetic material using theMg-containing oxide film-coated iron powder of the present invention isexplained.

A Mg-containing oxide film-coated iron powder of the present inventionmay be subjected to compacting and heat treatment in accordance with ausual method. The composite soft magnetic material produced using theMg-containing oxide film-coated iron powder of the present invention ispreferably constituted of an iron particle phase and grain boundaryphase surrounding the iron particle phase, where the grain boundaryphase contains Mg—Fe—O ternary-based oxide including crystallineMgO-dissolving wustite phase.

Alternatively, the soft magnetic material may be produced by preparing amixed powder such that 0.05 to 1% weight of one or two selected fromsilicon oxide and aluminum oxide each having a grain size of 0.5 μm orless and the balance consisting of the Mg-containing oxide film-coatediron powder of the present invention are blended in the mixed power,compacting, and heat-treating the mixed powder in accordance with theusual method. According to this production method, the Mg—Fe—Oternary-based oxide deposition film at least containing (Mg, Fe)O andconstituting the Mg-containing oxide film-coated iron powder of thepresent invention reacts with the silicon oxide and/or aluminum oxide toform a complex oxide. Therefore, it is possible to obtain a compositesoft magnetic material having a texture in which complex oxide of highresistance present in the grain boundary of the iron powder, and havinghigh resistivity. In addition, since the iron powder is heat-treatedinterposing the silicon oxide and/or aluminum oxide, it is possible toproduce a composite soft magnetic material having excellent mechanicalstrength. In this case, since the silicon oxide and/or the aluminumoxide have a main role in the heat treatment, a coercive force can bemaintained at a low value, and therefore, it is possible to produce acomposite soft magnetic material having low hysteresis loss. It ispreferable that the above-described heat treatment be performed at atemperature of 400 to 1300° C. in an inert gas atmosphere or in anoxidizing gas atmosphere.

In addition, a composite soft magnetic material may be produced bymixing the Mg-containing oxide film-coated iron powder of the presentinvention and a wet solution such as a sol-gel (silicate) solution ofsilica and sol-gel solution of alumina added to the powder, drying themixture of the powder and the solution, compacting the dried mixture,and heat-treating the compacted mixture at a temperature of 400 to 1300°C. in an inert gas atmosphere or in an oxidizing gas atmosphere.Preferably, these composite soft magnetic materials produced using theMg-containing oxide film-coated iron powder of the present invention areconstituted of an iron particle phase and grain boundary phasesurrounding the iron particle phase, where the grain boundary phaseincludes Mg—Fe—O ternary-based oxides including a crystallineMgO-dissolving wustite phase.

Moreover, a composite soft magnetic material having further improvedresistivity and strength may be produced by mixing the Mg-containingoxide film-coated iron powder of the present invention with an organicinsulating material, inorganic insulating material, or a mixture of anorganic insulating material and inorganic insulating material,compacting the mixed material, and heat-treating the compacted material.In this case, epoxy resin, fluororesin, phenol resin, urethane resin,silicone resin, polyester resin, phenoxy resin, urea resin, isocyanateresin, acrylic resin, polyimide resin or the like may be applied as theorganic insulating material. Phosphate such as iron phosphate, variousglassy insulating materials, water glass mainly composed of sodiumsilicate, insulating oxide or the like may be applied as the inorganicinsulating material.

In addition, a composite soft magnetic material may be produced bymixing the Mg-containing oxide film-coated iron powder of the presentinvention with one or two or more selected from boron oxide, vanadiumoxide, bismuth oxide, antimony oxide, and molybdenum oxide such that, inreduced mass of B₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 weight %is blended in the mixture, compacting the mixture, and heat-treating thecompact at a temperature of 500 to 1000° C. The thus produced compositesoft magnetic material has a composition containing, in reduced mass ofB₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO3, 0.05 to 1 weight % of one or moreselected from boron oxide, vanadium oxide, bismuth oxide, antimonyoxide, and molybdenum oxide, and the balance consisting of Mg-containingoxide film-coated iron powder of the present invention. In the compositesoft magnetic material, films are formed by the reaction of the Mg—Fe—Oternary-based oxide deposition films at least containing (Mg,Fe)O andone or more selected from boron oxide, vanadium oxide, bismuth oxide,antimony oxide, and molybdenum oxide.

The composite soft magnetic material may be produced by blending one ormore selected from a sol solution or powder of boron oxide, sol solutionor powder of vanadium oxide, sol solution or powder of bismuth oxide,sol solution or powder of antimony oxide, and sol solution or powder ofmolybdenum oxide such that the mixture has a composition containing, inreduced mass of B₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 weight %,and the balance consisting of Mg-containing oxide film-coated ironpowder of the present invention, mixing and drying the mixture, therebyproducing mixed-oxide film-coated iron powder made by coating the driedgel or powder of the mixed oxide on the Mg-containing oxide film-coatediron powder of the present invention, compacting and molding themixed-oxide-coated iron powder, and heat-treating the compact at atemperature of 500 to 1000° C. These composite soft magnetic materialshaving high resistivity and produced using the Mg-containing oxidefilm-coated iron powder of the present invention is preferablyconstituted of an iron particle phase and grain boundary phasesurrounding the iron particle phase, where the grain boundary phaseincludes Mg—Fe—O ternary-based oxide including crystallineMgO-dissolving wustite phase.

The composite soft magnetic material produced using the Mg-containingoxide film-coated iron powder of the present invention, has highdensity, high strength, and high magnetic flux density. The compositesoft magnetic material having high magnetic flux density and highfrequency core loss may be applied as a material of variouselectromagnetic circuit components utilizing the above-describedproperties. Examples of the above-described electromagnetic circuitcomponents include a magnetic core, core of a motor, core of agenerator, solenoid core, ignition core, reactor, transformer, core of achoke coil, and core of a magnetic sensor or the like. Theelectromagnetic circuit component comprising the composite soft magneticmaterial having high resistance and utilizing the Mg-containing oxidefilm-coated iron powder of the present invention may be equipped toelectric apparatuses such as a motor, generator, solenoid, injector,electromagnetic valve, inverter, converter, transformer, potentialtransformer, electric relay, magnetic sensor or the like, andcontributes to improving efficiency and performance, downsizing, andweight saving of the apparatuses.

The inventors performed research to manufacture a Mg-containing oxidefilm-coated iron powder having such properties that: the oxide film isfirmly bonded to the surface of iron powder particle, and when thepowder is press-molded, breakdown of a high resistance oxide film on thesurface of iron powder does not occur during the press molding; whenstrain-relief heat treatment at a high temperature is performed afterpress molding, surface insulation is not reduced, and the powder hashigh resistance, low eddy current loss; and a coercive force can befurther reduced and hysteresis loss can be reduced in the case ofperforming heat treatment of the powder for straightening annealing.

As a result, the below-described findings could be obtained. Firstly, aniron powder (hereafter referred to as oxidation-treated iron powder)having a surface coating of iron oxide is formed by heating an ironpowder in an oxidizing atmosphere. The oxidation-treated iron powder ismixed with an Mg powder, and the obtained mixed powder is subjected toheating in an inert gas atmosphere or in an vacuum atmosphere whiletumbling (rolling) the powder.

(F) By the above-described treatment, an Mg—Fe—O ternary-based oxidedeposition film is formed on the particle surface of the iron powdersuch that ultra-fine grains of metallic Fe are dispersed in the matrixof the Mg—Fe—O ternary-based oxide film. Since ultra-fine metallic Fegrains are dispersed in the matrix, the Mg—Fe—O ternary-based oxidedeposition film comprising ultra-fine grained metallic Fe dispersed inthe matrix has high toughness and is excellent in deformability comparedto the conventional Mg-containing ferrite film. In addition, in theMg-containing oxide film-coated iron powder coated with the Mg—Fe—Oternary-based oxide deposition film comprising ultra-fine grainedmetallic Fe particles dispersed in the matrix, since the extremely fineparticles of metallic iron are dispersed in the matrix of theMg-containing oxide film, the oxide deposition film has high toughnessand sufficiently tracks the deformation of iron powder particle, andremarkably excellent bonding to the iron particle compared to theconventional Mg-containing oxide film-coated iron powder in whichMg-containing ferrite is formed on the surface of the iron particle.Therefore, there is a lesser likelihood that particles of the ironpowder is made to contact with each other by the deformation of theoxide film as an insulation film occurring in the press molding.Therefore, even when strain-relief heat treatment at a high temperatureis performed after press molding the powder, the oxide film is escapedfrom deterioration of insulation property, and maintains highresistance. Therefore it is possible to obtain a composite soft magneticmaterial having low eddy current loss, further reduced coercive force inthe case of being subjected to the strain-relief heat treatment, havingreduced hysteresis loss, and therefore having low core loss.(G) The above-described Mg—Fe—O ternary-based oxide deposition filmcomprising ultra-fine grained metallic Fe grains dispersed in the matrixhas a concentration gradient such that Mg and O decrease from exteriorsurface to the interior direction, and Fe increase to the interior.(H) The above-described Mg—Fe—O ternary-based oxide deposition filmcomprising ultra-fine grained metallic Fe grains dispersed in the matrixincludes MgO-dissolving wustite phase (a material composed of solidsolution of MgO and wustite (FeO)).(I) More preferably, the MgO-dissolving wustite described in (H) has acrystalline structure.(J) A sulfur-enriched layer is formed in a boundary portion between theparticle of the iron powder and the Mg—Fe—O ternary-based oxidedeposition film comprising ultra-fine grained metallic Fe dispersed inthe matrix, where the sulfur concentration of the sulfur-enriched layeris higher than that of sulfur contained in a central portion of the ironpowder particle.(K) The Mg—Fe—O ternary-based oxide deposition film comprisingultra-fine grained metallic Fe dispersed in the matrix has a finecrystalline texture having a grain size of 200 nm or less.(L) It is preferable that the outermost surface of the above-describedMg—Fe—O ternary-based oxide deposition film formed on the surface of theiron powder particle and comprising ultra-fine grained metallic Fedispersed in the matrix is substantially composed of MgO.

The present invention is made based on the above-described findings andhas the following aspects.

(8) A Mg-containing oxide film-coated iron powder comprising iron powderparticles and Mg—Fe—O ternary-based oxide deposition films which includeultra-fine metallic Fe grains dispersed in the matrix and are coated onsurfaces of the iron powder particles.

(9) A Mg-containing oxide film-coated iron powder as described in (8),wherein the Mg—Fe—O ternary-based oxide deposition films includingultra-fine metallic Fe grains dispersed in the matrix have concentrationgradients where Mg and O decrease from the exterior surfaces to interiordirection, and Fe increases towards the interior direction.(10) A Mg-containing oxide film-coated iron powder as described in theabove-described (8) or (9), wherein the Mg—Fe—O ternary-based oxidedeposition films including ultra-fine metallic Fe grains dispersed inthe matrix have a MgO-dissolving wustite phase in matrices.(11) A Mg-containing oxide film-coated iron powder as described in theabove-described (10), wherein the MgO-dissolving wustite phase iscrystalline MgO-dissolving wustite phase.(12) A Mg-containing oxide film-coated iron powder as described in theabove-described (8), (9), (10) or (11), further comprisingsulfur-enriched layers in boundary portions between the iron powderparticles and the Mg—Fe—O ternary-based oxide deposition films includingultra-fine metallic Fe grains dispersed in the matrix, wherein sulfurconcentrations of the sulfur-enriched layers are higher than that ofsulfur contained as unavoidable impurities in central portions of theiron powder particles.(13) A Mg-containing oxide film-coated iron powder as described in (8),(9) (10), (11), or (12), wherein the above-described Mg—Fe—Oternary-based oxide deposition films including ultra-fine metallic Fegrains dispersed in the matrix have microcrystalline structures having agrain size of 200 nm or less.(14) A Mg-containing oxide film-coated iron powder as described in (8),(9) (10), (11), (12), or (13), wherein outermost surfaces of the Mg—Fe—Oternary-based oxide deposition films including ultra-fine metallic Fegrains dispersed in the matrix are substantially composed of MgO.

The Mg-containing oxide film-coated iron powder of the present inventionas described in the above-described (8) to (13) is produced by forming aoxidation-treated iron powder by heating iron powder in an oxidizingatmosphere, adding Mg powder to the oxidation-treated iron powder andmixing the powder, and heating thus obtained mixed powder in an inertgas atmosphere or in a vacuum atmosphere while tumbling the mixedpowder.

More practically, oxidation-treated iron powder having iron oxide filmsformed on the surfaces of iron powder particles is produced bypreliminary heating the iron powder in an oxidizing atmosphere at atemperature of 50 to 500° C. Mg powder is added to and mixed with theoxidation-treated iron powder. While being rolled, obtained mixed powderis heated at a temperature of 150 to 1100° C. in an inert gas atmosphereor in a vacuum atmosphere having a pressure of 1×10⁻¹² to 1×10⁻¹ MPa.Thus the above-described powder of the present invention may beproduced.

The Mg—Fe—O ternary-based oxide deposition film comprising ultra-finegrained metallic Fe dispersed in the matrix and having an outermostsurface substantially composed of MgO as described in theabove-described (14) may be produced by: forming a relatively thick ironoxide film on the particle surface of the iron powder by preliminaryheating the iron powder at a temperature of 50 to 500° C. in anoxidizing atmosphere for relatively long duration; adding further largeamount of Mg powder is added to the oxidation-treated iron powder havingthe relatively thick iron oxide film and mixing the powder; and heatingthus obtained mixed powder at a temperature of 150 to 1100° C. in aninert gas atmosphere having a pressure of 1×10⁻¹² to 1×10⁻¹ MPa or in avacuum atmosphere, while tumbling the mixed powder.

In general, “deposition film” is a term denoting a film made of vacuumevaporated or sputtered film-forming atoms deposited on the surface of,for example, a substrate. In the present invention, the Mg—Fe—Oternary-based oxide deposition film formed on the surface of the ironpowder of the present invention and comprising ultra-fine grainedmetallic Fe particles in the matrix denotes a film deposited on thesurface of particles of the iron powder being accompanied with areaction of Mg and iron oxide (Fe—O) on the particle surface of theoxidation-treated iron powder Since ultra-fine metallic Fe grains aredispersed in the matrix of the Mg-containing oxide film comprisingMg—Fe—O ternary-based oxide, the Mg—Fe—O ternary-based oxide depositionfilm according to the present invention, comprising ultra-fine grainedmetallic Fe particles dispersed in the matrix has a high toughness.Therefore, the deposition film sufficiently tracks the deformation ofthe iron powder particle at the time of press molding, and hasremarkably excellent adherence to the iron powder particle. In addition,the Mg—Fe—O ternary-based oxide deposition film according to the presentinvention, comprising ultra-fine grained metallic Fe grains dispersed inthe matrix preferably contains MgO-dissolving wustite. More preferably,the MgO-dissolving wustite has a crystalline structure.

Preferably, the Mg—Fe—O ternary-based oxide deposition film formed onthe surface of the iron powder particle of the present invention andcomprising ultra-fine grained metallic Fe grains dispersed in the matrixhas a film-thickness in a range from 5 to 500 nm so as to ensure highmagnetic flux density and high resistivity of the composite softmagnetic material formed by compacting the powder. Where the filmthickness is smaller than 5 nm, it is not preferable, since theresistivity is not sufficient and eddy current loss is increased in thecomposite soft magnetic material formed by compacting the powder. On theother hand, where the film thickness is larger than 500 nm, it is notpreferable since the magnetic flux density is decreased in the compositesoft magnetic material formed by compacting the powder. More preferably,the film thickness is in a range from 5 to 200 nm.

The Mg—Fe—O ternary-based oxide deposition film constituting theMg-containing oxide-coated iron powder of the present invention andcomprising ultra-fine grained metallic Fe particles dispersed in thematrix preferably has a concentration gradient such that Mg and Odecrease from exterior surface to the interior direction, and Feincrease to the interior. Because of such a concentration gradient, theoxide film has further excellent adherence to the iron powder.Therefore, there is a lesser possibility of breakdown of the oxide filmas the insulation film during the press molding of the powder. The oxidefilm escapes from deterioration of insulation property and maintainshigh resistance even when the press-molded powder is subjected tostrain-relief heat treatment at a high temperature. Therefore, eddycurrent loss is lowered.

In addition, a sulfur-enriched layer containing a higher concentrationof sulfur than the sulfur concentration of the central portion of theiron particle of the iron powder exists in the boundary portion betweenthe iron particle and the Mg—Fe—O ternary-based oxide deposition filmcomprising ultra-fine grained metallic Fe dispersed in the matrix. Bythe presence of such a sulfur-enriched layer in the boundary portion,the oxide film has further excellent bonding to the iron powder.Therefore, the deposition film tracks the deformation of the particleduring compacting the powder, and breakdown of the coating is inhibited.At the time of heat treatment, iron powder particles are prevented frombeing made to contact and bonded with each other, and resistivity of theoxide film is maintained. Therefore, eddy current loss is lowered. It isconsidered that the sulfur in the sulfur-enriched layer is provided fromunavoidable impurities contained in the iron powder.

The Mg—Fe—O ternary-based oxide deposition film constituting theMg-containing oxide-coated iron powder of the present invention andcomprising ultra-fine grained metallic Fe grains dispersed in the matrixpreferably has as small a grain size as possible, and preferably hasultra-microcrystalline structure having a grain size of 200 nm or less.By the presence of such an ultra-fine grained crystalline texture, theultra-fine grained crystalline deposition film tracks the deformation ofpowder particle at the time of compacting the powder, and breakdown ofthe coating is inhibited. In addition, the powder is prevented frombeing made to contact with each other even at the time of heattreatment. Even when the compacted powder is subjected to strain-reliefheat treatment at a high temperature, the oxide is stable, be preventedfrom reduction of insulation property, and maintains high resistance.Therefore, eddy current loss is lowered. Where the grain size is largerthan 200 nm, film thickness of the deposition film exceeds 500 nm, andmagnetic flux density of the composite soft magnetic material isreduced.

The Mg—Fe—O ternary-based oxide deposition film comprising ultra-finemetallic Fe grains dispersed in the matrix preferably contains as high aMgO content as possible in the outermost surface. Most preferably, theoutermost surface of the film is substantially composed of MgO. Wherethe outermost surface of the film is substantially MgO, at the time ofheat treatment of the press-molded compact, diffusion of Fe isinhibited, the iron powder particles are prevented from contacting andbonding with each other, and reduction of insulation property isprevented, high resistance is maintained, and eddy current loss islowered.

The Mg—Fe—O ternary-based oxide deposition film constituting theMg-containing oxide-coated iron powder of the present invention andcomprising ultra-fine grained metallic Fe particles dispersed in thematrix may be a pseudo ternary oxide deposition film in which Mg ispartially replaced by one or more selected from Al, Si, Mn, Zn, Cu, andCo such that 10 atomic % or less of Mg is replaced.

In the Mg-containing oxide film-coated iron powder of the presentinvention, it is preferable to use a powder having a mean grain size ina range from 5 to 500 μm. The reason is explained as follows. Where themean grain size is smaller than 5 μm, it is not preferable, sincecompressibility of the powder is lowered, volume fraction of the powderis lowered, and therefore magnetic flux density is lowered. On the otherhand, where the mean grain size is too larger than 500 μm, eddy currentin the interior of the powder particle is increased and magneticpermeability at high frequency is reduced.

The composite soft magnetic material according to the present inventionhaving higher resistivity than that of the conventional one can beproduced by press molding and heat-treating the Mg-containing oxidefilm-coated iron powder of the present invention in accordance with theusual process. A texture of the thus produced composite soft magneticmaterial of the present invention is constituted of an iron particlephase generated from the iron powder and grain boundary phasesurrounding the iron particle phase. The above-described grain boundaryphase contains Mg—Fe—O ternary-based oxide including MgO-dissolvingwustite. More preferably, the MgO-dissolving wustite is a crystallineone.

Otherwise, the composite soft magnetic material may be produced byproducing a mixed powder such that 0.05 to 1 mass % of one or twoselected from silicon oxide and aluminum oxide having a mean grain sizeof 0.5 μm or less and the balance consisting of theMg-containing-oxide-film-coated iron powder according to the presentinvention are blended and mixed in the mixed powder; compacting andheat-treating the mixed powder in accordance with the usual method.

In accordance with this production method, the Mg—Fe—O ternary-basedoxide deposition film constituting the Mg-containing oxide film-coatediron powder of the present invention and comprising ultra-fine grainedmetallic Fe grains dispersed in the matrix reacts with silicon oxideand/or aluminum oxide and forms complex oxide. As a result, thecomposite soft magnetic material having high resistivity, in whichcomplex oxide having high resistance exists in grain boundary of theiron powder, is obtained. In addition, because of the presence ofsilicon oxide and/or aluminum oxide at the time of heat treatment, thecomposite soft magnetic material having high mechanical strength can beproduced. In this case, since the silicon oxide and/or aluminum oxidehave a main roll in the heat treatment, small value of coercive forcecan be maintained. Therefore it is possible to produce a composite softmagnetic material having low hysteresis loss. Preferably, theabove-described heat treatment is performed in an inert gas atmosphereor in an oxidizing gas atmosphere at a temperature of 400 to 1300° C.

In addition, a composite soft magnetic material may be produced bymixing the Mg-containing oxide film-coated iron powder of the presentinvention and a wet solution such as a sol-gel (silicate) solution ofsilica and sol-gel solution of alumina added to the powder, drying themixture of the powder and the solution, compacting the dried mixture,and heat-treating the compacted mixture at a temperature of 400 to 1300°C. in an inert gas atmosphere or in an oxidizing gas atmosphere. Morepreferably, these composite soft magnetic materials of the presentinvention has a texture constituted of an iron particle phase generatedfrom the iron powder and grain boundary phase surrounding the ironparticle phase, where the grain boundary phase contains Mg—Fe—Oternary-based oxide including MgO-dissolving wustite, and theMgO-dissolving wustite has a crystalline structure.

Moreover, a composite soft magnetic material having further improvedresistivity and strength may be produced by mixing the Mg-containingoxide film-coated iron powder of the present invention with an organicinsulating material, inorganic insulating material, or a mixture oforganic insulating material and inorganic insulating material. In thiscase, epoxy resin, fluororesin, phenol resin, urethane resin, siliconeresin, polyester resin, phenoxy resin, urea resin, isocyanate resin,acrylic resin, polyimide resin or the like may be applied as the organicinsulating material. Phosphate such as iron phosphate, various glassyinsulating materials, water glass mainly composed of sodium silicate,insulating oxide or the like may be applied as the inorganic insulatingmaterial.

In addition, a composite soft magnetic material may be produced bymixing the Mg-containing oxide film-coated iron powder of the presentinvention with one or two or more selected from boron oxide, vanadiumoxide, bismuth oxide, antimony oxide, and molybdenum oxide such that, inreduced mass of B₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 mass % isblended on the mixture, compacting the mixture, and heat-treating thecompact at a temperature of 500 to 1000° C. The thus produced compositesoft magnetic material has a composition containing, in reduced mass ofB₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 mass % of one or moreselected from boron oxide, vanadium oxide, bismuth oxide, antimonyoxide, and molybdenum oxide, and the balance consisting of Mg-containingoxide film-coated iron powder of the present invention. In the compositesoft magnetic material, films are formed by the reaction of the Mg—Fe—Oternary-based oxide deposition films comprising extremely fine grainedmetallic Fe particles dispersed in the matrix and one or more selectedfrom boron oxide, vanadium oxide, bismuth oxide, antimony oxide, andmolybdenum oxide.

The composite soft magnetic material may be produced by blending one ormore selected from a sol solution or powder of boron oxide, sol solutionor powder of vanadium oxide, sol solution or powder of bismuth oxide,sol solution or powder of antimony oxide, and sol solution or powder ofmolybdenum oxide such that the mixture has a composition containing, inreduced mass of B₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 mass %,and the balance consisting of Mg-containing oxide film-coated ironpowder of the present invention, mixing and drying the mixture, therebyproducing mixed-oxide film-coated iron powder made by coating the driedgel or powder of the mixed oxide on the Mg-containing oxide film-coatediron powder of the present invention, compacting and molding themixed-oxide-coated iron powder, and heat-treating the compact at atemperature of 500 to 1000° C.

The composite soft magnetic materials produced in accordance with theabove-described method using Mg-containing oxide film-coated iron powderof the present invention are each constituted of an iron particle phasegenerated from the iron powder in the Mg-containing oxide film-coatediron powder, and grain boundary phase surrounding the iron particlephase. The grain boundary phase contains Mg—Fe—O ternary-based oxidesincluding MgO-dissolving wustite. More preferably, the above-describedMgO-dissolving wustite has a crystalline structure.

The composite soft magnetic material produced using the Mg-containingoxide film-coated iron powder of the present invention, has highdensity, high strength, and high magnetic flux density. The compositesoft magnetic material having high magnetic flux density and low coreloss at high frequency may be applied as a material of variouselectromagnetic circuit components utilizing the above-describedproperties. Examples of the above-described electromagnetic circuitcomponents include a magnetic core, core of a motor, core of agenerator, solenoid core, ignition core, reactor, transformer, core of achoke coil, and core of a magnetic sensor or the like.

The electromagnetic circuit component comprising the composite softmagnetic material having high resistance and utilizing the Mg-containingoxide film-coated iron powder of the present invention may be equippedto electric apparatuses such as a motor, generator, solenoid, injector,electromagnetic valve, inverter, converter, transformer, potentialtransformer, electric relay, magnetic sensor or the like, andcontributes to improving efficiency and performance, downsizing, andweight saving of the apparatuses.

The inventors performed research to manufacture a high resistancefilm-coated iron powder having such properties that: the high resistancefilm is firmly bonded to the surface of iron powder, and when the powderis press-molded, breakdown of a high resistance oxide film on thesurface of iron powder particle does not occur during the press molding;when strain-relief heat treatment at high temperature is performed afterpress molding, surface insulation is not reduced, and the powder hashigh resistance, low eddy current loss; and a coercive force can befurther reduced and hysteresis loss can be reduced in the case ofperforming heat treatment of the powder for straightening annealing. Asa result, the below-described findings could be obtained.

(M) Firstly, by performing phosphating treatment of iron powder, ironpowder having phosphate film formed on the particle surface of the ironpowder (hereafter referred to as phosphate-coated iron powder) isproduced. Mg powder is added to and mixed with the phosphate-coated ironpowder. By performing heat treatment of the obtained mixed powder in aninert gas atmosphere or in a vacuum atmosphere while tumbling the mixedpowder, it is possible to obtain a deposition film-coated iron powderhaving a surface coating of deposition film composed of Mg, Fe, P, andO. The deposition film composed of Mg, Fe, P, and O contains Mg—Fe—P—Oquaternary phosphate compound composed of Mg, Fe, P, and O and Mg—Fe—Oternary-based oxide composed of Mg, Fe, and O, and fine iron phosphidegrains dispersed in the matrix.(N) Since the fine iron phosphide grains are dispersed in the matrix,the deposition film of the above-described deposition film-coated ironpowder has high toughness. Therefore, compared with the Mg-containingferrite film formed on the surface of conventional oxide-film coatediron powder, the above-described deposition film easily tracksdeformation of the iron powder particle at the time of press molding thepowder. In addition, since the deposition film has remarkably excellentadherence to the iron powder particle, there is a lesser possibility ofbreakdown of the deposition film as an insulation film, and the ironpowder is scarcely made to contact with each other. Even when thepress-molded deposition film-coated iron powder is subjected tostrain-relief heat treatment at a high temperature, there is a lesserpossibility of occurring reduction of insulation property of thedeposition film. Therefore, high resistance is maintained, and eddycurrent loss is lowered. In addition, in the case of performingstrain-relief heat treatment, coercive force is further reduced andhysteresis loss is lowered, and therefore it is possible to obtain acomposite soft magnetic material having low core loss.(O) Mg—Fe—P—O quaternary phosphate compound and Mg—Fe—O ternaly oxideincluded in the above-described deposition film include MgO-dissolvingwustite phase.(P) The above-described deposition film having fine iron phosphideparticles dispersed in the matrix preferably has a microcrystallinestructure having a grain size of 200 nm or less.

The present invention is made based on the above-described findings andhas the following aspects.

(18) A deposition film-coated iron powder comprising iron particles anddeposition films which comprise Mg, Fe, P, and O and are coated onsurfaces of the iron particles.

(19) A deposition film-coated iron powder as described in (18), whereinthe deposition films comprise Mg—Fe—P—O quaternary-based phosphatescomposed of Mg, Fe, P, and O, Mg—Fe—O ternary-based oxides composed ofMg, Fe, and O, and fine iron phosphide grains dispersed in the matrix.(20) A deposition film-coated iron powder as described in (18) or (19),wherein the Mg—Fe—P—O quaternary phosphates and Mg—Fe—O ternary-basedoxides included in the deposition film include crystalline Mg—0dissolving wustite type phase.(21) A deposition-film-coated iron power as described in (18), (19) or(20), wherein the deposition films have microcrystalline structureshaving a grain size of 200 nm or less.

As described above, deposition film-coated iron powder of the presentinvention as described in the above (18) to (21) is formed by: adding Mgpowder to phosphate-coated iron powder and mixing the powder; heatingthe obtained mixed powder in an inert gas atmosphere or in a vacuumatmosphere while tumbling the mixed powder; and further performingoxidation treatment of the powder in an oxidizing atmosphere. Morepractically, the above-described deposition film-coated iron powder maybe produced by: adding Mg powder to phosphate-coated iron powder andmixing the powder; heating the obtained mixed powder at a temperature of150 to 1100° C. in an inert gas atmosphere having a pressure of 1×10⁻¹²to 1×10⁻¹ MPa or in a vacuum atmosphere while tumbling the mixed powder;and further performing oxidation treatment of the powder in an oxidizingatmosphere.

In general, “deposition film” is a term denoting a film made of vacuumevaporated or sputtered film-forming atoms deposited on the surface of,for example, a substrate. In the present invention, the deposition filmformed on the iron powder of the present invention denotes a filmdeposited on the surface of the particles of iron powder beingaccompanied with a reaction of Mg and iron phosphate (Fe—P—O) on thesurface of the phosphate-coated iron particles. Since fine grains ofiron phosphide are dispersed in the matrix of the deposition film formedon the surface of the iron powder of the present invention and includingfine iron phosphide grains dispersed in the matrix has a high toughness.Therefore, the deposition film sufficiently tracks the deformation ofthe iron powder particle at the time of press molding of the powder, andhas remarkably excellent adherence to the iron powder.

Preferably, the deposition film formed on the particle surface of theiron powder of the present invention has a film-thickness in a rangefrom 5 to 500 nm so as to ensure high magnetic flux density and highresistivity of the composite soft magnetic material formed by compactingthe powder. Where the film thickness is smaller than 5 nm, it is notpreferable, since the resistivity is not sufficient and eddy currentloss is increased in the composite soft magnetic material formed bycompacting the powder. On the other hand, where the film thickness islarger than 500 nm, it is not preferable since the magnetic flux densityis decreased in the composite soft magnetic material formed bycompacting the powder. More preferably, the film thickness is in a rangefrom 5 to 200 nm.

The Mg—Fe—P—O quaternary-based phosphate and Mg—Fe—O ternary-based oxideincluded in the deposition film constituting the deposition film-coatediron powder of the present invention preferably include crystallineMg-dissolving wustite type phase. Preferably, the crystallineMg-dissolving wustite type phase has a NaCl type crystal structure,while in some case, Fe and/or Mg of are partially replaced by P.

The deposition film constituting the deposition film-coated iron powderof the present invention preferably has as small a grain size aspossible, and preferably has microcrystalline structure having a grainsize of 200 nm or less. By the presence of such a microcrystallinestructure, the fine grained crystalline deposition film tracks thedeformation of the powder at the time of compacting the powder therebybeing prevented from breakdown. In addition, the powder is preventedfrom being made to contact with each other even at the time of heattreatment. Even when the compacted powder is subjected to strain-reliefheat treatment at high temperature, the oxide is stable, be preventedfrom reduction of insulation property, and maintains high resistance.Therefore, eddy current loss is lowered. Where the grain size is largerthan 200 nm, it is not preferable since film thickness of the depositionfilm exceeds 500 nm, and magnetic flux density of the composite softmagnetic material is reduced.

Iron powder as a raw material for producing the deposition film-coatediron powder of the present invention preferably has a mean grain size ina range from 5 to 500 μm. The reason is explained as follows. Where themean grain size is smaller than 5 μm, compressibility of the powder isreduced, and volume fraction of the powder is lowered, and therefore thevalue of the magnetic flux density is lowered. On the other hand, wherethe mean grain size is too larger than 500 μm, eddy current in theinterior of the powder particle is increased and magnetic permeabilityat high frequency is reduced.

The Mg—Fe—P—O quaternary phosphate comprising Mg, Fe, P, and O and theMg—Fe—O ternary-based oxide comprising Mg, Fe, and O, both constitutingthe deposition film-coated iron powder of the present invention may be apseudo ternary-based oxide deposition film in which Mg is partiallyreplaced by one or more selected from Al, Si, Mn, Zn, Cu, and Co suchthat 10% or less of Mg is replaced.

Next, a method of producing a soft magnetic material utilizing thedeposition-film coated iron powder of the present invention is explainedin the following.

The composite soft magnetic material can be produced by press moldingand heat-treating the deposition film-coated iron powder of the presentinvention in accordance with the usual process. Otherwise, the compositesoft magnetic material may be produced by producing a mixed powder byadding one or two selected from silicon oxide and aluminum oxide havinga mean grain size of 0.5 μm and in an amount of 0.05 to 1 mass % to thedeposition-film-coated iron powder according to the present invention,and compacting and heat-treating the mixed powder in accordance with theusual method.

Where the composite soft magnetic material is produced by theabove-described method, it is possible to obtain a composite softmagnetic material in which silicon oxide and/or aluminum oxide bond thedeposition film-coated iron powder where iron powder is surrounded by adeposition film including Mg—Fe—P—O quaternary-based phosphatecomprising Mg, Fe, P, and O and Mg—Fe—O ternary-based oxide comprisingMg, Fe, and O, and fine iron phosphide particles dispersed in thematrix. Since the composite soft magnetic material is heat-treatedthrough silicon oxide and/or aluminum oxide, it is possible to furtherenhance the mechanical strength.

In this case, since the silicon oxide and/or aluminum oxide have a mainroll in the heat treatment, small value of coercive force can bemaintained. Therefore it is possible to produce a composite softmagnetic material having low hysteresis loss. Preferably, theabove-described heat treatment is performed in an inert gas atmosphereor in an oxidizing gas atmosphere at a temperature of 400 to 1300° C.

In addition, a composite soft magnetic material may be produced bymixing the deposition film-coated iron powder of the present inventionand a wet solution such as a sol-gel (silicate) solution of silica andsol-gel solution of alumina added to the powder, drying the mixture ofthe powder and the solution, compacting the dried mixture, andheat-treating the compacted mixture at a temperature of 400 to 1300° C.in an inert gas atmosphere or in an oxidizing gas atmosphere.

Moreover, a composite soft magnetic material having further improvedresistivity and strength may be produced by mixing the depositionfilm-coated iron powder of the present invention with an organicinsulating material, inorganic insulating material, or a mixture oforganic insulating material and inorganic insulating material. In thiscase, epoxy resin, fluororesin, phenol resin, urethane resin, siliconeresin, polyester resin, phenoxy resin, urea resin, isocyanate resin,acrylic resin, polyimide resin or the like may be applied as the organicinsulating material. Phosphate such as iron phosphate, various glassyinsulating materials, water glass mainly composed of sodium silicate,insulating oxide or the like may be applied as the inorganic insulatingmaterial.

In addition, a composite soft magnetic material may be produced bymixing the deposition film-coated iron powder of the present inventionwith one or two or more selected from boron oxide, vanadium oxide,bismuth oxide, antimony oxide, and molybdenum oxide such that, inreduced mass of B₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 mass % isblended in the mixture, compacting the mixture, and heat-treating theobtained compact at a temperature of 500 to 1000° C. The thus producedcomposite soft magnetic material has a composition containing, inreduced mass of B₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 mass % ofone or more selected from boron oxide, vanadium oxide, bismuth oxide,antimony oxide, and molybdenum oxide, and the balance consisting ofdeposition film-coated iron powder of the present invention. In thecomposite soft magnetic material, films are formed by the reaction ofthe deposition films and one or more selected from boron oxide, vanadiumoxide, bismuth oxide, antimony oxide, and molybdenum oxide.

The composite soft magnetic material may be produced by blending one ormore selected from a sol solution or powder of boron oxide, sol solutionor powder of vanadium oxide, sol solution or powder of bismuth oxide,sol solution or powder of antimony oxide, and sol solution or powder ofmolybdenum oxide such that the mixture has a composition containing, inreduced mass of B₂O₃, V₂O₅, Bi₂O₃, Sb₂O₃, and MoO₃, 0.05 to 1 weight %,and the balance consisting of the above-described deposition film-coatediron powder of the present invention, mixing and drying the mixture,thereby producing mixed-oxide film-coated iron powder made by coatingthe dried gel or powder of the mixed oxide on the above-describeddeposition film-coated iron powder of the present invention, compactingand molding the mixed-oxide-coated iron powder, and heat-treating thecompact at a temperature of 500 to 1000° C.

The composite soft magnetic materials having high resistivity andproduced in accordance with the above-described method using thedeposition film-coated iron powder of the present invention are eachconstituted of an iron particle phase and grain boundary phasesurrounding the iron particle phase. The grain boundary phase preferablycontains oxides including crystalline MgO-dissolving wustite type phase.The crystalline Mg-dissolving wustite type phase preferably has a NaCltype crystal structure, while in some case, Fe and/or Mg of arepartially replaced by P.

The composite soft magnetic material produced using the depositionfilm-coated iron powder of the present invention, has high density, highstrength, and high magnetic flux density. The composite soft magneticmaterial having high magnetic flux density and low core loss at highfrequency may be applied as a material of various electromagneticcircuit components utilizing the above-described properties. Examples ofthe above-described electromagnetic circuit components include amagnetic core, core of a motor, core of a generator, solenoid core,ignition core, reactor, transformer, core of a choke coil, and core of amagnetic sensor or the like. The electromagnetic circuit componentcomprising the composite soft magnetic material having high resistanceand utilizing the deposition film-coated iron powder of the presentinvention may be equipped to electric apparatuses such as a motor,generator, solenoid, injector, electromagnetic valve, inverter,converter, transformer, potential transformer, electric relay, magneticsensor or the like, and contributes to improving efficiency andperformance, downsizing, and weight saving of the apparatuses.

The inventors performed research so as to obtain a insulationfilm-coated iron silicide powder having such properties that: theinsulation film is firmly bonded to the surface of iron silicide powder,and when the powder is press-molded, breakdown of insulation film on thesurface of iron silicide powder does not occur during the press molding;when heat treatment is performed after the press molding, surfaceinsulation of the iron silicide powder is not reduced.

As a result, the below-described findings could be obtained.

(Q) An oxide deposition film-coated iron silicide powder havingMg—Si—Fe—O quaternary-based oxide deposition film comprising Mg, Si, Fe,and O formed on the particle surface of the iron silicide powder can beobtained by: adding Mg powder to a surface oxidized iron silicide powder(here and hereafter, which includes an iron silicide powder having aspontaneously oxidized surface and an iron silicide powder having anoxide film formed on the surface) and mixing the powder, heating theobtained mixed powder in an inert gas atmosphere or in a vacuumatmosphere, and where necessary, performing second oxidizing treatmentto heat the powder in an oxidizing atmosphere. Compared to theconventional chemical conversion film-coated iron silicide film having achemical conversion film formed on the surface of the iron silicidepowder, the oxide deposition film-coated iron silicide powder shows anremarkably excellent adherence of the Mg—Si—Fe—O quaternary-based oxidedeposition film to the surface of the iron silicide powder. Therefore,there is a lesser possibility that the Mg—Si—Fe—O quaternary-based oxidedeposition film as an insulation film is broken down during the pressmolding and particles of the iron silicide powder are made to contactwith each other. Therefore, even when the press-molded powder issubjected to strain-relief heat treatment at a high temperature, theinsulation property of the Mg—Si—Fe—O quaternary-based oxide depositionfilm is not reduced and its high resistance is maintained. Therefore,eddy current loss is lowered. In addition, since the coercive force canbe further reduced by the heat treatment for reducing strain, hysteresisloss can be reduced to a lower level. Therefore, a composite softmagnetic material of low core loss can be obtained.(R) The above-described Mg—Si—Fe—O quaternary-based oxide depositionfilm has a concentration gradient such that contents of Mg and Oincrease towards the surface and Fe content decrease towards thesurface, and has a concentration gradient where Si content increases inthe vicinity of the outermost surface such that a portion close to theoutermost surface shows as a high Si content.(S) Preferably, the above-described Mg—Si—Fe—O quaternary-based oxidedeposition film includes crystalline MgO-dissolving wustite type phase.(T) The above-described Mg—Si—Fe—O quaternary-based oxide depositionfilm has a fine crystalline texture having a grain size of 200 nm orless.(U) The above-described Mg—Si—Fe—O quaternary-based oxide depositionfilm includes metallic Fe or Fe—Si alloy.

The present invention was made based on the above-described findings andhas the following aspects.

(24) An oxide deposition film-coated iron silicide powder comprisingiron silicide powder particles and Mg—Si—Fe—O quaternary-based oxidedeposition films which comprise Mg, Si, Fe, and O and are formed onsurfaces of the iron silicide powder particles.

(25) An oxide deposition film-coated iron silicide powder as describedin (24), wherein the above-described Mg—Si—Fe—O quaternary-based oxidedeposition films has a have concentration gradients where contents of Mgand O increase towards the surface and Fe contents decrease towards thesurfaces, and have concentration gradients of Si where Si contentsincrease in the vicinity of the outermost surfaces such that portionsclose to the outermost surface show high Si contents.(26) An oxide deposition film-coated iron silicide powder as describedin the above (24) or (25), wherein the Mg—Si—Fe—O quaternary-based oxidedeposition films include a crystalline MgO-dissolving wustite typephase.(27) An oxide deposition film-coated iron silicide powder as describedin the above (24), (25) or (26), wherein the Mg—Si—Fe—O quaternary-basedoxide deposition films include metallic Fe or Fe—Si alloy.(28) An oxide deposition film-coated iron silicide powder as describedin the above (24), (25), (26), or (27), wherein the Mg—Si—Fe—Oquaternary-based oxide deposition films have microcrystalline structureshaving a grain size of 200 nm or less.

As an iron silicide powder used in the production of the above-describedoxide deposition film-coated iron silicide powder of the presentinvention as described in the above (24), (25), (26) or (27), ironsilicide powder having a composition containing Si: 0.1 to 10 weight %,and the balance consisting of Fe and unavoidable impurities is used.This composition is a generally known composition. Therefore, thepresent invention has the following aspect.

(29) An deposition film-coated iron silicide powder as described in theabove (24), (25), (26), (27), and (28), wherein the above-described ironsilicide powder have a composition containing Si: 0.1 to 10 mass % and abalance consisting of Fe and unavoidable impurities.

The oxide deposition film-coated iron silicide powder of the presentinvention as described in the above (24), (25), (26), (27), (28), and(29) may be produced by: adding Mg powder to the iron silicide powderhaving the above-described composition and having a surface oxide filmand mixing the powder; heating the obtained mixed powder at atemperature of 150 to 1100° C. under an inert gas atmosphere or a vacuumatmosphere having a pressure of 1×10⁻¹² to 1×10⁻¹ MPa; and wherenecessary, performing second oxidizing treatment of the powder to heatthe powder for a long duration in an oxidizing atmosphere.

The above-described iron silicide powder having an surface oxide filmmay be obtained by leaving the iron silicide powder produced bygas-atomizing, water-atomizing, or gas-water-atomizing, and having acomposition containing Si: 0.1 to 10 weight % and the balance consistingof Fe and unavoidable impurities to stand in air atmosphere, or beperforming oxidizing treatment of the iron silicide powder. Since theiron silicide powder obtained by gas-atomizing or gas-water-atomizinghas nearly spherical shape, the powder is appropriate to obtain acomposite soft magnetic material having a relatively high resistance. Onthe other hand, since the iron silicide powder obtained bywater-atomizing has an uneven surface shape of powder, the powder isappropriate to obtain a composite soft magnetic material having arelatively high strength.

In general, the term “oxide deposition film” indicates an oxide filmformed by depositing vacuum-evaporated or sputtered film-forming atoms,for example, on a substrate. In the present invention, the Mg—Si—Fe—Oquaternary oxide deposition film formed on the surface of iron silicidepowder denotes a film formed on the surfaces of particles of the ironsilicide powder being accompanied by reaction of Mg and surface oxidefilm of the surface-oxidized iron silicide powder.

The oxide deposition film formed on the surface of iron silicide powderpreferably has a film thickness in a range from 5 nm to 500 nm so as toensure a high magnetic flux density and high resistivity of a compositesoft magnetic material formed by compacting the powder. Where the filmthickness is smaller than 5 nm, it is not preferable, because thecomposite soft magnetic material formed by compacting the powder cannothave a sufficient resistivity and has an increased eddy current loss. Onthe other hand, where the film thickness is larger than 500 nm, it isnot preferable because the composite soft magnetic material formed bycompacting the powder has a decreased magnetic flux density. Morepreferably, the film thickness may be in a range of 5 nm to 200 nm.

Since the Mg—Si—Fe—O quaternary-based oxide film formed on the surfaceof the oxide deposition film-coated iron silicide powder of the presentinvention has a concentration gradient such that contents of Mg and Oincrease towards the surface and Fe content decrease towards thesurface, adherence of the Mg—Si—Fe—O quaternary-based oxide depositionfilm to the iron silicide powder is improved. In addition, adherence ofthe Mg—Si—Fe—O quaternary-based oxide deposition film to the ironsilicide powder is improved by the presence of metallic iron or Fe—Sialloy included in the film. Therefore, in the oxide depositionfilm-coated iron silicide powder if the present invention having such anMg—Si—Fe—O quaternary-based oxide deposition film, breakdown ordelamination of the film do not occur in the process such as pressmolding, and therefore, composite soft magnetic material having highresistance can be obtained.

It is preferable that the Mg—Si—Fe—O quaternary-based oxide depositionfilm formed on the surface of the oxide deposition film-coated ironsilicide powder of the present invention includes crystallineMg-dissolving wustite type phase. Most preferably, the above-describedcrystalline Mg-dissolving wustite type phase has an NaCl type structure.

The Mg—Si—Fe—O quaternary oxide deposition film formed on the surface ofthe oxide deposition film-coated iron silicide powder of the presentinvention preferably has as small a grain size as possible, andpreferably has microcrystalline structure having a grain size of 200 nmor less. By the presence of such a microcrystalline structure, the finegrained crystalline oxide deposition film tracks the deformation of thepowder at the time of compacting the powder thereby being prevented frombreakdown. In addition, the iron silicide powder particles are preventedfrom being made to contact with each other even at the time of heattreatment. Even when the compacted powder is subjected to strain-reliefheat treatment at a high temperature, the oxide is stable, be preventedfrom reduction of insulation property, and maintains high resistance.Therefore, eddy current loss is lowered. Where the grain size is largerthan 200 nm, it is not preferable since the magnetic flux density of thecomposite soft magnetic material is reduced. More preferable grain sizeis 50 nm or less.

Iron silicide powder described in (29) used for producing the depositionoxide film-coated iron silicide powder as described in the above (24) to(28) preferably has a mean grain size in a range from 5 to 500 μm. Thereason is explained as follows. Where the mean grain size is smallerthan 5 μm, compressibility of the powder is reduced, and volume fractionof the powder is lowered, and therefore the value of the magnetic fluxdensity is lowered. On the other hand, where the mean grain size is toolarger than 500 μm, eddy current in the interior of the powder particleis increased and magnetic permeability at high frequency is reduced.More preferably, the deposition oxide film-coated iron silicide powderas described in the above (20) to (27) has a mean grain size in a rangefrom 5 to 100 μm.

A composite soft magnetic material may be produced by compacting theoxide deposition film-coated iron silicide powder of the presentinvention, and heat-treating the obtained compact at a temperature of500 to 1000° C.

A composite soft magnetic material having improved resistivity andstrength may be produced by compacting and heat-treating the oxidedeposition film-coated iron silicide powder of the present inventionmixed with an organic insulating material or inorganic insulatingmaterial. In this case, epoxy resin, fluororesin, phenol resin, urethaneresin, silicone resin, polyester resin, phenoxy resin, urea resin,isocyanate resin, acrylic resin, polyimide resin, polyphenylene sulfideresin (hereafter referred to as PPS resin) or the like may be applied asthe organic insulating material. Among these organic insulatingmaterial, silicone resin, poyimid resin, or PPS resin are especiallypreferred. It is possible to add an appropriate amount of plasticizerfor controlling the hardness of binder, coupling agent for enhancing thebonding between the binder and the powder. It is possible to addlubricant such as stearic acid, various stearate or the like so as toimprove sliding of the powder during compacting the powder, and toensure the insulation of the deposition film. In addition, it ispossible to add glass binder as the inorganic insulating material.

Accordingly, the present invention has the following aspects.

(30) A composite soft magnetic material comprising a heat-treatedcompact of the oxide-deposition film coated iron silicide powder asdescribed in the above (24), (25), (26), (27), (28) or (29).

(31) A composite soft magnetic material comprising a heat-treatedcompact including the oxide deposition film-coated iron silicide powderas described in the above (24), (25), (26), (27), (28) or (29), andinterparticle insulating material composed of silicone resin, polyimideresin, or PPS resin.

It is preferable that the composite soft magnetic material producedusing the deposition oxide film-coated iron silicide powder of thepresent invention as described in the above (24), (25), (26), (27), (28)or (29) is constituted of iron silicide phase and grain boundary phasesurrounding the iron silicide phase, and the grain boundary phaseincludes Mg—Si—Fe—O quaternary oxide containing MgO-dissolving wustitetype phase. Therefore, the present invention has the following aspect.

(32) A composite soft magnetic material as described in the above (30)or (31), comprising iron silicide phase, grain boundary phasesurrounding the iron silicide phase, wherein the grain boundary phaseincludes Mg—Si—Fe—O quaternary oxide containing MgO-dissolving wustitetype phase.

The composite soft magnetic material produced using the oxide depositionfilm-coated iron silicide powder of the present invention, has highdensity, high strength, and high magnetic flux density. The compositesoft magnetic material having high magnetic flux density and low coreloss at high frequency may be applied as a material of variouselectromagnetic circuit components utilizing the above-describedproperties. Examples of the cores of the above-described electromagneticcircuit components include a magnetic core, core of a motor, core of agenerator, solenoid core, ignition core, reactor, transformer, core of achoke coil, and core of a magnetic sensor or the like. Theelectromagnetic circuit component comprising the composite soft magneticmaterial having high resistance and utilizing the oxide depositionfilm-coated iron silicide powder of the present invention may beequipped to electric apparatuses such as a motor, generator, solenoid,injector, electromagnetic valve, inverter, converter, potentialtransformer, electric relay, magnetic sensor system or the like, andcontributes to improving efficiency and performance, downsizing, andweight saving of the apparatuses.

Recently, based on a consideration of an environmental issue,counter-steps for energy saving have been performed in the fields ofgeneral consumer electronics, automobiles, and industrial machineries.Therefore, there is a demand for enhancing the effect of electriccircuit components. Among these, the reactor is known as a componentused for transforming potential, that is, stepping up or stepping downthe potential, of electric power source of automobile, controlling theimpedance, and power supply for filter. For the reactor, in order toachieve a small size and low loss, a composite soft magnetic materialhaving high saturation magnetization, high resistance and low coerciveforce. In order to improve DC superposed property, stable magneticpermeability is preferred. The core of the reactor is provided with agap and is designed such that a predetermined inductance can be obtainedirrespective of fluctuation of input current within a working range.

Where a reactor have a core material composed of the composite softmagnetic material comprising a heat-treated compact of the oxidedeposition film-coated iron silicide powder of the present invention ora heat-treated compact including the oxide deposition film-coated ironsilicide powder and interparticle insulating material composed ofsilicone resin, polyimide resin, or PPS resin, since insulation ismaintained and a coercive force is reduced even when the core materialis subjected to high temperature heat treatment for strain reduction,loss is reduced in the high frequency region and intermediate to lowfrequency region, and the reactor has an excellent alternating currentproperty. Therefore, the reactor may be used as a reactor having smallsize, low loss, low noise and being excellent in DC superpositionproperty, and may be applied as a reactor for transforming potential,that is, stepping up or stepping down the potential, of electric powersource of automobile, controlling the impedance, and power supply forfilter, or the like.

The inventors performed research so as to obtain an oxide film-coatediron-based Fe—Si-based soft magnetic powder having such properties that:when the powder is press-molded, breakdown of a high resistance oxidefilm on the surface of the iron-based Fe—Si-based soft magnetic powderdoes not occur during the press molding, and the high resistancematerial film is firmly bonded to the surface; when high temperatureheat treatment is performed after the press molding, surface insulationis not reduced; and the powder has high resistance, low eddy currentloss; and a coercive force can be further reduced and hysteresis losscan be further reduced.

As a result, the below-described findings could be obtained.

Firstly, by adding Si powder to an iron-based Fe—Si-based soft magneticpowder or to a Fe powder, mixing the powder, and heating the mixedpowder in an non-oxidizing atmosphere, iron-based Fe—Si-based softmagnetic powder is produced such that the powder has a highconcentration Si diffused layer on the surface of the iron-basedFe—Si-based soft magnetic powder or the Fe powder, where concentrationof Si in the high concentration Si diffused layer is higher than that ofthe iron-based Fe—Si-based soft magnetic powder or of the Fe powder. Byperforming oxidization treatment of the obtained iron-based Fe—Si-basedsoft magnetic material having the high concentration Si diffused layer,surface oxidized high concentration Fe—Si iron-based soft magneticpowder having an oxide layer on the high concentration Si diffused layeris produced. By adding Mg powder to the surface oxidized highconcentration iron-based Fe—Si-based soft magnetic powder and mixing thepowder, and heating the obtained mixed powder at a temperature of 150 to1100° C. under an inert gas atmosphere or a vacuum atmosphere having apressure of 1×10⁻¹² to 1×10⁻¹ MPa, an oxide deposition film comprisingMg, Si, Fe, and O is formed on the surface of the Fe—Si iron-based softmagnetic powder.

(V) With respect to Mg contained in the oxide deposition film comprisingMg, Si, Fe, and O, Mg shows a concentration gradient such that Mgcontent increases towards the outermost surface. With respect to O, Oshows a concentration gradient such that O content increases towards theoutermost surface. On the other hand, Fe shows a concentration gradientsuch that Fe content decreases towards the outermost surface. Withrespect to Si, in the vicinity to the outer most surface of thedeposition film, Si shows a concentration gradient such that Si contentincreases towards the outermost surface.(W) In the above-described oxide deposition film comprising Mg, Si, Fe,and O, Mg and O are contained in the matrix as MgO-dissolving wustite (amaterial constituted of a solid solution of MgO and wustite (FeO)),partial amounts of Fe and Si are contained as metallic Fe or Fe—Sialloy. Since, the above-described oxide deposition film comprising Mg,Si, Fe, O includes metallic Fe, the film has toughness, and easilytracks the deformation of powder at the time of compacting the powder.(X) Since the above-described oxide deposition film comprising Mg, Si,Fe, and O has a fine crystalline texture having a grain size of 200 nmor less, the film has toughness and easily tracks the deformation ofpowder at the time of compacting the powder.

Compared to the conventional Mg-containing ferrite oxide film coatediron-based Fe—Si-based soft magnetic powder having Mg-containing ferriteoxide film formed on the surface of the iron-based Fe—Si-based softmagnetic powder, the iron-based Fe—Si-based soft magnetic powder havingthe oxide deposition film comprising Mg, Si, Fe, and O formed on thesurface is remarkably excellent in the adherence of the oxide powder tothe iron-based Fe—Si-based soft magnetic powder. Therefore, there is alesser possibility that oxide films as insulation films are deformed andparticles of the iron-based Fe—Si-based soft magnetic powder are made tocontact with each other. In addition, the above-described oxidedeposition film comprising Mg, Si, Fe, and O is chemically more stablethan the Mg-containing ferrite oxide film. Therefore, even when thepress-molded powder is subjected to strain-relief heat treatment at ahigh temperature, insulation property of the oxide deposition film isnot deteriorated, high resistance is maintained, and eddy current lossis lowered. By further performing strain relief heat treatment, coerciveforce is further reduced, and it is possible to depress the hysteresisloss to a low value. Therefore, it is possible to obtain a compositesoft magnetic material having low core loss.

The present invention made on the results of the above-describedresearch, and has the following aspects.

(35) An oxide deposition film-coated iron-based Fe—Si-based softmagnetic powder comprising iron-based Fe—Si-based soft magnetic powderparticles and oxide deposition films which comprise Mg, Si, Fe, and Oand are formed on surfaces of the iron-based Fe—Si-based soft magneticpowder particles.(36) An oxide-deposition film-coated iron-based Fe—Si-based softmagnetic powder as described in the above (35), wherein the iron-basedFe—Si-based soft magnetic powder particles have a composition containingSi: 0.1 to 10 mass %, and the balance consisting of Fe and unavoidableimpurities.(37) An oxide-deposition film-coated iron-based Fe—Si-based softmagnetic powder as described in the above (35) or (36), wherein theoxide deposition films comprising Mg, Si, Fe and O have concentrationgradients where contents of Mg and O increase towards the surfaces andFe contents decrease towards the surfaces, and have concentrationgradients of Si where Si contents increase in the vicinities of theoutermost surfaces such that portions close to the outermost surfacesshow high Si contents.(38) An oxide deposition film-coated iron-based Fe—Si-based softmagnetic powder as described in the above (35), (36) or (37), whereinthe oxide deposition films comprising Mg, Si, Fe and O includecrystalline Mg-dissolving wustite type phase, and include metallic Fe orFe—Si alloy.(39) An oxide deposition film-coated iron-based Fe—Si-based softmagnetic powder as described in the above (35), (36), (37), or (38),wherein the oxide deposition films comprising Mg, Si, Fe and O have amicrocrystalline structure having a mean grain size of 200 nm or less.

In general, the term “oxide deposition film” indicates an oxide filmformed by depositing vacuum-evaporated or sputtered film-forming atoms,for example, on a substrate. In the present invention, the oxidedeposition film comprising Mg, Si, Fe and O and formed on the surfacesof iron-based Fe—Si-based soft magnetic powder denotes a film depositedon the surface of particles of the iron-based Fe—Si-based soft magneticpowder being accompanied by reaction of Mg and Si on the surface ofparticles of iron-based Fe—Si-based soft magnetic powder. The oxidedeposition film comprising Mg, Si, Fe and O and formed on the surface ofiron-based Fe—Si-based soft magnetic powder preferably has a filmthickness in a range from 5 nm to 500 nm so as to ensure a high magneticflux density and high resistivity of a composite soft magnetic materialformed by compacting the powder. Where the film thickness is smallerthan 5 nm, it is not preferable, because the composite soft magneticmaterial formed by compacting the powder cannot have sufficientresistivity and has an increased eddy current loss. On the other hand,where the film thickness is larger than 500 nm, it is not preferablebecause the composite soft magnetic material formed by compacting thepowder has a decreased magnetic flux density. More preferably, the filmthickness may be in a range from 5 nm to 200 nm.

It is preferable that the grain size of crystals constituting oxidedeposition film comprising Mg, Si, Fe and O and formed on the surface ofiron-based Fe—Si-based soft magnetic powder as described in the above(35) to (39) is as small as possible. Preferably, the deposition filmhas a fine crystalline texture having a grain size of 200 nm or less.Because of such a fine crystalline texture, the fine crystalline oxidedeposition film tracks the deformation of powder particle at the time ofcompacting the powder, and the film is prevented from breakdown. At thetime of heat treatment, particles of the iron-base Fe—Si-based softmagnetic powder particles are prevented from contacting and bonding witheach other. When the compacted powder is subjected to strain-relief heattreatment at a high temperature, because of the stable property of theoxide, reduction of insulation is prevented, and eddy current loss islowered. Where the grain size is larger than 200 nm, it is notpreferable, because the magnetic flux density of compacted compositesoft magnetic material is reduced.

In the production of the oxide deposition film-coated iron-basedFe—Si-based soft magnetic powder as described in the above (35) to (39),it is preferable to use the powder having a mean grain size in a rangefrom 5 to 500 μm. The reason for this limitation is explained asfollows. Where the mean grain size is smaller than 5 μm, it is notpreferable, because the compressibility of the powder is lowered andvolume fraction of the powder is decreased, and therefore the value ofmagnetic flux density is lowered. On the other hand, where the meangrain size is too larger than 500 μm, eddy current in the interior ofpowder particle is increased, and magnetic permeability at highfrequency is reduced.

A composite soft magnetic material having further improved resistivityand strength may be produced by mixing the above-described oxidedeposition film-coated iron-based Fe—Si-based soft magnetic powder ofthe present invention with an organic insulating material, inorganicinsulating material, or a mixture of organic insulating material andinorganic insulating material, compacting the mixed material, andheat-treating the compacted material. In this case, epoxy resin,fluororesin, phenol resin, urethane resin, silicone resin, polyesterresin, phenoxy resin, urea resin, isocyanate resin, acrylic resin,polyimide resin, PPS resin or the like may be applied as the organicinsulating material. Phosphate such as iron phosphate, various glassyinsulating materials, water glass mainly composed of sodium silicate,insulating oxide or the like may be applied as the inorganic insulatingmaterial.

In addition, a composite soft magnetic material may be produced bycompacting the oxide deposition film-coated iron-based Fe—Si-based softmagnetic powder of the present invention, and heat-treating the obtainedcompact at a temperature of 500 to 1000° C.

The composite soft magnetic material produced using the oxide depositionfilm-coated iron-based Fe—Si-based soft magnetic powder of the presentinvention, has high density, high strength, high resistivity, and highmagnetic flux density. The composite soft magnetic material having highmagnetic flux density and high frequency core loss may be applied as amaterial of various electromagnetic circuit components utilizing theabove-described properties. Examples of the above-describedelectromagnetic circuit components include a magnetic core, core of amotor, core of a generator, solenoid core, ignition core, reactor,transformer, core of a choke coil, and core of a magnetic sensor or thelike. The electromagnetic circuit component comprising the compositesoft magnetic material having high resistance and utilizing the oxidedeposition film-coated iron-based Fe—Si-based soft magnetic powder ofthe present invention may be equipped to electric apparatuses such as amotor, generator, solenoid, injector, electromagnetic valve, inverter,converter, potential transformer, electric relay, magnetic sensor systemor the like, and contributes to improving efficiency and performance,downsizing, and weight saving of the apparatuses.

Moreover, so as to solve the above-described problems, the inventorspreviously invented Mg-containing iron oxide film-coated iron powdersuch as described in the following (a) to (e).

(a) A Mg-containing iron oxide film-coated iron powder having a coatingsof Mg—Fe—O ternary-based oxide deposition films at least containing(Mg,Fe)O on the surface of iron powder particles.

(b) A Mg-containing iron oxide film-coated iron powder having coatingsof Mg—Fe—O ternary-based oxide deposition films at least containing(Mg,Fe)O on the surfaces of iron powder particles, havingsulfur-enriched layers in the boundary portions between the iron powderparticles and the Mg—Fe—O ternary-based oxide deposition films at leastcontaining (Mg,Fe)O, wherein the sulfur concentrations of thesulfur-enriched layers are higher than that of sulfur contained in acentral portions of the iron powder particles.(c) A Mg-containing oxide film-coated iron powder as described in theabove (a) or (b), wherein (Mg,Fe)O included in the Mg—Fe—O ternary-basedoxide deposition films is a crystalline MgO-dissolving wustite phase.(d) A Mg-containing iron oxide film-coated iron powder as described inthe above (a), (b) or (c), wherein the Mg—Fe—O ternary-based oxidedeposition films at least containing (Mg, Fe)O have microcrystallinestructures having a grain size of 200 nm or less.(e) A Mg-containing iron oxide film-coated iron powder as described inthe above-described (a), (b), (c) or (d), wherein outermost surfaces ofthe Mg—Fe—O ternary-based oxide deposition films at least containing(Mg, Fe)O are substantially composed of MgO.

The previously invented Mg-containing iron oxide film-coated ironpowders as described in the above (a), (b), (c), (d) or (e) wereobtained by: firstly forming an iron powder (hereafter referred to asoxidation-treated iron powder) having a surface coating of iron oxide bysubjecting the iron powder to an oxidization treatment, for example,heating the iron powder in an oxidizing atmosphere; adding an Mg powderto the oxidation-treated iron powder and mixing the powder; subjectingthe obtained mixed powder to heating or the like in an inert gasatmosphere or in an vacuum atmosphere; and further performing a secondoxidization treatment to heat the powder in an oxidizing atmosphere. Theinvention of these previously invented Mg-containing iron oxidefilm-coated iron powder were made based on the findings such asdescribed in the following.

(Y) MgO—FeO—Fe₂O₃ ternary-based oxide is represented by, for example,(Mg, Fe)O and (Mg, Fe)₃O₄. Among this generally known Mg—Fe—Oternary-based oxide, at least (Mg, Fe)O is contained in a Mg—Fe—Oternary-based oxide deposition film which is formed on the surface ofiron powder. The Mg-containing oxide film-coated iron powder having asurface coating of the Mg—Fe—O ternary-based oxide deposition filmcontaining at least (Mg, Fe)O is remarkably superior in bonding of theoxide film to the iron particle compared with the conventionalMg-containing oxide film-coated iron powder formed by coating anMg-containing ferrite on the surface of iron powder. Therefore, there isa lesser possibility that the oxide film as an insulation film is brokendown during the press molding and particles of the iron powder are madeto contact with each other. Therefore, even when the press-molded powderis subjected to strain-relief heat treatment at a high temperature, theinsulation property of the oxide film is not reduced and high resistanceis maintained. Therefore, eddy current loss is lowered. In addition,since the coercive force can be further reduced by further performingstrain relief heat treatment, hysteresis loss can be reduced to a lowerlevel. Therefore, a composite soft magnetic material of low core losscan be obtained.(Z) It is preferable that the (Mg,Fe)O contained in the Mg—Fe—Oternary-based oxide deposition film of the above-described Mg-containingoxide film-coated iron powder is a crystalline MgO-dissolving wustite (asolid solution of MgO and wustite (FeO)).(Γ) A sulfur-enriched layer is formed in a boundary portion between theiron powder particle and the Mg—Fe—O ternary-based oxide deposition filmat least containing (Mg,Fe)O, where the sulfur concentration of thesulfur-enriched layer is higher than that of sulfur contained in acentral portion of the iron powder as an unavoidable impurity.(Δ) The above-described Mg—Fe—O ternary-based oxide deposition film atleast containing (Mg, Fe)O has a fine crystalline texture having a grainsize of 200 nm or less.(Θ) It is preferable that an outer-most surface of the above-describedMg—Fe—O ternary-based oxide deposition film at least containing (Mg,Fe)O contain as much MgO as possible. Most preferably, the outer-mostsurface is substantially composed of MgO.

The Mg-containing iron oxide film-coated iron powder of the previousinvention as described in (a) to (d) can be produced by: firstlyproducing an oxidizing-treated iron powder by forming an iron oxide filmon the surface of iron powder by heating the iron powder at atemperature of 50 to 500° C. in an oxidizing atmosphere; adding Mgpowder to the oxidizing-treated iron powder and mixing the powder;heating the obtained mixed powder at a temperature of 150 to 1100° C. inan inert atmosphere having a gas pressure of 1×10⁻¹² to 1×10⁻¹ MPa or ina vacuum atmosphere; and where necessary, further performing a secondoxidizing treatment after heating the mixed powder at a temperature of50 to 350° C. in an oxidizing atmosphere.

The Mg—Fe—O ternary-based oxide deposition film containingMgO-dissolving wustite phase and having an outermost surfacesubstantially composed of MgO as described in the above (e) may beproduced by: firstly producing an oxidizing-treated iron powder byforming an iron oxide film on the surface of iron powder by heating theiron powder at a temperature of 50 to 500° C. in an oxidizingatmosphere; adding a Mg powder of a further large amount to theoxidizing-treated iron powder and mixing the powder; heating the mixedpowder at a temperature of 150 to 1100° C. in an inert atmosphere havinga gas pressure of 1×10⁻¹² to 1×10⁻¹ MPa or in a vacuum atmosphere; andfurther performing a second oxidizing treatment to heat the mixed powderfor a further long duration in an oxidizing atmosphere.

In Mg-wustite contained in the Mg—Fe—O ternary-based oxide depositionfilm formed on the surface of the previously invented Mg-containing ironoxide film-coated iron powder of the above described (a) to (e), contentof oxygen is not limited by the ratio of (Mg,Fe):O=1:1, but may have arange of solubility.

In general, the term “deposition film” indicates a film formed bydepositing vacuum-evaporated or sputtered film-forming atoms, forexample, on a substrate. In the present invention, the Mg—Fe—Oternary-based oxide deposition film at least containing (Mg,Fe)O andformed on the surface of iron powder denotes a film deposited on thesurface of iron powder particle being accompanied by reaction of Mg andiron oxide (Fe—O) on the surface of the iron powder particle having aniron oxide film. The Mg—Fe—O ternary-based oxide deposition film atleast containing (Mg,Fe)O and formed on the surface of iron powderpreferably has a film thickness in a range from 5 nm to 500 nm so as toensure a high magnetic flux density and high resistivity of a compositesoft magnetic material formed by compacting the powder. Where the filmthickness is smaller than 5 nm, it is not preferable, because thecomposite soft magnetic material formed by compacting the powder cannothave a sufficient resistivity, and eddy current loss is increased. Onthe other hand, where the film thickness is larger than 500 nm, it isnot preferable because magnetic flux density is decreased in thecomposite soft magnetic material formed by compacting the powder. Morepreferably, the film thickness may be in a range of 5 nm to 200 nm.

The Mg—Fe—O ternary-based oxide film at least containing (Mg, Fe)Oformed on the surface of the previously invented Mg-containing ironoxide film-coated iron powder as described in the above (a) to (e) has asulfur-enriched layer at the boundary portion between the Mg—Fe—Oternary-based oxide film at least containing (Mg, Fe)O and the ironpowder particle, where the sulfur concentration of the sulfur-enrichedlayer is higher than that of sulfur contained in a central portion ofthe iron powder particle. The presence of the sulfur-enriched layer maybe confirmed by performing analysis of the sulfur concentration by Augerelectron spectroscopy, showing the results of the analysis, where a peakof the sulfur concentration is shown in the graph. By the presence ofsuch a sulfur-enriched layer at the boundary portion, the Mg—Fe—Oternary-based oxide film at least containing (Mg, Fe)O has furtherimproved bonding to the surface of iron powder, breakdown of thedeposition film is prevented by tracking of the deposition film todeformation of the powder at the time of press molding the powder. Highresistance is maintained by preventing contact and bonding of ironpowder particles with each other at the time of heat treatment, andtherefore eddy current loss is reduced. The iron powder contains sulfuras unavoidable impurities. It is considered that most of the sulfur inthe sulfur-enriched layer is provided by the sulfur contained in thesurface portion of the iron powder.

It is preferable that the grain size of crystals constituting theMg—Fe—O ternary-based oxide deposition film at least containing (Mg,Fe)O and formed on the surface of the Mg-containing iron oxidefilm-coated iron powder of the above (a) to (e) is as small as possible.Preferably, the deposition film has a fine crystalline texture having agrain size of 200 nm or less. Because the film has such a finecrystalline texture, the fine crystalline Mg—Fe—O ternary-based oxidedeposition film tracks the deformation of powder particle at the time ofcompacting the powder, and is prevented from breakdown. At the time ofheat treatment, the iron powder is prevented from being made to contactand bonded with each other. When the powder is subjected tostrain-relief heat treatment at a high temperature, because of thestable property of the oxide, reduction of insulation is prevented, highresistance is maintained, and eddy current loss is lowered. Where thegrain size is larger than 200 nm, it is not preferable, because the filmthickness of the Mg—Fe—O ternary-based oxide deposition film exceeds 500nm, and magnetic flux density of compacted composite soft magneticmaterial is reduced.

The MgO content in the outermost surface of the Mg—Fe—O ternary-basedoxide deposition film at least containing (Mg, Fe)O and formed on thesurface of the Mg-containing iron oxide film-coated iron powder of theabove (e) is preferably as high as possible. It is most preferable thatthe outermost surface is substantially composed of MgO. Where theoutermost surface is substantially MgO, diffusion of Fe is inhibited atthe time of heat treatment of the press-molded compact, the iron powderparticles are prevented from contacting and bonding with each other,reduction of insulation is prevented, high resistance is ensured, andeddy current loss is lowered.

In the above-description, previously invented Mg-containing iron oxidefilm-coated iron powder as described in (a) to (e) is explained. Anobject of the present invention is to provide a composite soft magneticpowder having further improved compressibility and sinterability, and amethod of producing the powder. Such a powder may be provided by furthercoating MgO—SiO₂ composite oxide film having a MgO/SiO₂ value in a rangefrom 1.0 to 3.0 in molar ratio on the surface of the previously inventedMg-containing iron oxide film-coated iron powder as described in (a) to(e).

In general, MgO—SiO₂ composite oxide film has a high electric insulationproperty and relatively soft hardness (1 to 4 in Mohs hardness), isenriched in antifrictional action and lubricating action, and acts aslubricant at the time of compacting the powder.

Therefore, the composite soft magnetic powder having MgO—SiO₂ oxidedeposition film formed on the surface of the previously inventedMg-containing iron oxide film-coated iron powder as described in theabove (a) to (e) has further improved compressibility. In addition,since a melting point of MgO—SiO₂ composite oxide film is lower thanthat of MgO, composite soft magnetic powder of the present inventionhaving MgO—SiO₂ oxide deposition film coated on the particle surface ofthe Mg-containing iron oxide film-coated iron powder as described in theabove (a) to (e) has further improved sinterability.

Accordingly, the present invention has the following aspects.

(48) A composite soft magnetic powder comprising: Mg-containing ironoxide film-coated iron powder particles having iron powder particles andMg—Fe—O ternary-based oxide deposition films which contain at least (Mg,Fe)O and are formed on surfaces of the iron powder particles; andMgO—SiO₂ composite oxide film which have a MgO/SiO₂ value in a rangefrom 1.0 to 3.0 in molar ratio and are further coated on surfaces of theMg-containing iron oxide film-coated iron powder particles.(49) A composite soft magnetic powder comprising: Mg-containing ironoxide film-coated iron powder particles having iron powder particles,Mg—Fe—O ternary-based oxide deposition films which contain at least (Mg,Fe)O and are coated on surfaces of the iron powder particles, andsulfur-enriched layers in boundary portions between the iron powderparticles and the Mg—Fe—O ternary-based oxide deposition films at leastcontaining (Mg, Fe)O; and MgO—SiO₂ composite oxide films which have aMgO/SiO₂ value in a range from 1.0 to 3.0 in molar ratio and are furthercoated on surfaces of the Mg-containing iron oxide film-coated ironpowder particles, wherein sulfur concentrations of the sulfur-enrichedlayers are higher than that of sulfur contained as an unavoidableimpurity in central portions of the iron powder particles.(50) A composite soft magnetic powder as described in the above (48) or(49), wherein (Mg,Fe)O included in the Mg—Fe—O ternary-based oxidedeposition films of the above-described Mg-containing iron oxidefilm-coated iron powder is a crystalline MgO-dissolving wustite phase.(51) A composite soft magnetic powder as described in the above (48),(49) or (50), wherein the Mg—Fe—O ternary-based oxide deposition filmsat least containing (Mg,Fe)O have microcrystalline structures having agrain size of 200 nm or less.(52) A composite soft magnetic powder as described in theabove-described (48), (49), (50) or (51), wherein outermost surfaces ofthe Mg—Fe—O ternary-based oxide deposition films at least containing(Mg,Fe)O are substantially composed of MgO.

The composite soft magnetic powder of the present invention as describedin the above (48), (49), (50), (51) and (52) may be produced by:preparing a mixed oxide sol-solution of MgO and SiO₂ obtained by mixing,in volumetric ratio, alkoxysilane solution:1 and magnesium-alkoxidesolution:1 to 3; adhering the sol-solution to the surface of theMg-containing iron oxide film-coated iron powder as described in theabove (a) to (e); and heating and drying the powder.

(53) A composite soft magnetic material comprising an iron particlephase and grain boundary phase surrounding the iron particle phase,wherein the grain boundary phase contains Mg—Fe—O ternary-based oxideincluding a crystalline MgO-dissolving wustite phase.

In order to solve the above-described problem the inventors previouslyinvented Mg-containing oxide film-coated iron powder such as describedin the following (f) to (k).

(f) A Mg-containing oxide film-coated iron powder comprising iron powderparticles and Mg—Fe—O ternary-based oxide deposition films which includefine grained metallic Fe grains dispersed in the matrix and are coatedon surfaces of the iron powder particles.(g) A Mg-containing oxide film-coated iron powder comprising iron powderparticles coated with Mg—Fe—O ternary-based oxide deposition films,wherein the Mg—Fe—O ternary-based oxide deposition films include finegrained metallic Fe grains dispersed in the matrix and haveconcentration gradients such that Mg and O decrease from exteriorsurfaces to the interior direction, and Fe increases to the interiordirection.(h) A Mg-containing oxide film-coated iron powder comprising iron powderparticles coated with Mg—Fe—O ternary-based oxide deposition films asdescribed in the above (f), or (g), having sulfur-enriched layers inboundary portions between the iron powder particles and the Mg—Fe—Oternary-based oxide deposition films, where the sulfur-enriched layerscontain higher concentration of sulfur than that of sulfur contained incentral portions of the iron powder particles.(i) A Mg-containing oxide film-coated iron powder as described in theabove (f), (g), or (h), wherein the Mg—Fe—O ternary-based oxidedeposition films comprising ultra-fine metallic Fe grains in the matrixhave a crystalline MgO-dissolving wustite phase in the matrix.(j) A Mg-containing oxide film-coated iron powder as described in (f),(g) (h), or (i), wherein the above-described Mg—Fe—O ternary-based oxidedeposition films comprising ultra-fine metallic Fe grains dispersed inthe matrix have a microcrystalline structure having a grain size of 200nm or less.(k) A Mg-containing oxide film-coated iron powder as described in theabove (f), (g) (h), (i), or (j), wherein the outermost surfaces of theabove-described Mg—Fe—O ternary-based oxide deposition films comprisingultra-fine grained metallic Fe dispersed in the matrix are substantiallycomposed of MgO.

The previously invented Mg-containing oxide film-coated iron powder asdescribed in the above (f), (g), (h), (i), (j), or (k) is obtained by:firstly forming an iron powder (hereafter referred to asoxidation-treated iron powder) having a surface coating of iron oxide byperforming oxidization treatment, for example, by heating the ironpowder in an oxidizing atmosphere; adding Mg powder to theoxidation-treated iron powder and mixing the powder; heating thusobtained mixed powder in an inert gas atmosphere or in a vacuumatmosphere while tumbling the mixed powder; and further performingsecond oxidization treatment of the powder by heating the powder in anoxidizing atmosphere.

The obtained Mg—Fe—O ternary-based oxide deposition film of thepreviously invented Mg-containing iron oxide-coated iron powder wasformed based on the findings as described in the following.

(Λ) Compared with the conventional Mg-containing iron oxide film made byforming Mg-containing ferrite film on the surface of iron powder througha chemical process, the oxide deposition film has remarkably excellentbonding to the iron powder particle. Therefore, there is a lesserlikelihood that the iron particles are made to contact with each otherby the deformation of the oxide film as an insulation film occurring inthe press molding. Even when a high temperature finding for reducingstrain is performed after press molding the powder, the oxide film isescaped from deterioration of insulation property, and maintains highresistance, and eddy current loss is lowered. By further performing heattreatment, coercive force is further reduced. Therefore, hysteresis lossis reduced to a lower level, and a composite soft magnetic materialhaving a low core loss can be obtained.(Ω) The above-described Mg—Fe—O ternary-based oxide deposition filmcomprises fine metallic Fe grains dispersed in the matrix and has aconcentration gradient such that Mg and O decrease from exterior surfaceto the interior direction, and Fe increase to the interior direction.(Π) In the above-described Mg-containing iron oxide film-coated ironpowder, a sulfur-enriched layer is formed in a boundary portion betweenthe iron powder and the Mg—Fe—O ternary-based oxide deposition filmcomprising ultra-fine metallic Fe grains dispersed in the matrix, wherethe sulfur concentration of the sulfur-enriched layer is higher thanthat of sulfur contained in a central portion of the iron powder asunavoidable impurities.(Σ) The above-described Mg—Fe—O ternary-based oxide deposition filmcomprising ultra-fine grained metallic Fe particles dispersed in thematrix includes MgO-dissolving wustite phase (a material composed ofsolid solution of MgO and wustite (FeO)).(Φ) The above-described Mg—Fe—O ternary-based oxide deposition filmcomprising ultra-fine grained metallic Fe dispersed in the matrix has afine crystalline texture having a grain size of 200 nm or less.(Ψ) It is preferable that the outermost surface of the above-describedMg—Fe—O ternary-based oxide deposition film contains as high an amountof MgO, and most preferably, the outermost surface is substantiallycomposed of MgO.

More practically, a production process of the previously inventedMg-containing iron oxide film-coated iron powder as described in theabove (f) to (j) can be explained as following. Firstly,oxidation-treated iron powder having an iron oxide film formed on thesurface of iron powder is produced by preliminary heating the ironpowder in an oxidizing atmosphere at a temperature of 50 to 500° C. Mgpowder is added to and mixed with the oxidation-treated iron powder.While being rolled, obtained mixed powder is heated at a temperature of150 to 1100° C. in an inert gas atmosphere or in a vacuum atmospherehaving a pressure of 1×10⁻¹² to 1×10⁻¹ MPa. After that, where necessary,a second oxidization treatment is further performed, where the powder isheated at a temperature of 50 to 350° C. in an oxidizing atmosphere.

In the previously invented Mg—Fe—O ternary-based oxide deposition filmcomprising ultra-fine grained metallic Fe dispersed in the matrix andhaving an outermost surface substantially composed of MgO as describedin the above-described (k) may be produced by: forming anoxidation-treated iron powder having an iron oxide film formed on thesurface of iron powder by preliminary heating the iron powder in anoxidizing atmosphere at a temperature of 50 to 500° C.; adding furtherlarge amount of Mg powder to the oxidation-treated iron powder havingthe relatively thick iron oxide film and mixing the powder; heating thusobtained mixed powder at a temperature of 150 to 1100° C. in an inertgas atmosphere or in a vacuum atmosphere having a pressure of 1×10⁻¹² to1×10⁻¹ MPa, while tumbling the mixed powder; and further performingsecond oxidization treatment where the powder is heated at a temperatureof 50 to 350° C. in an oxidizing atmosphere for a further long duration.

In general, “deposition film” is a term denoting a film made of vacuumevaporated or sputtered film-forming atoms deposited on the surface of,for example, a substrate. In the present invention, the Mg—Fe—Oternary-based oxide deposition film formed on the surface of the ironpowder of the present invention and comprising ultra-fine grainedmetallic Fe particles in the matrix denotes a film deposited on thesurface of the iron powder particle being accompanied with a reaction ofMg and iron oxide (Fe—O) on the surface of the oxidation-treated ironpowder. Since extremely fine particles of metallic Fe are dispersed inthe matrix of the Mg-containing oxide film comprising Mg—Fe—Oternary-based oxide, the Mg—Fe—O ternary-based oxide deposition filmaccording to the present invention, comprising ultra-fine grainedmetallic Fe particles dispersed in the matrix has a high toughness.Therefore, the deposition film sufficiently tracks the deformation ofthe iron powder at the time of press molding, and has remarkablyexcellent adherence to the iron powder. In addition, the Mg—Fe—Oternary-based oxide deposition film according to the present invention,comprising ultra-fine grained metallic Fe particles dispersed in thematrix preferably contains MgO-dissolving wustite. More preferably, theMgO-dissolving wustite has a crystalline structure.

Preferably, the Mg—Fe—O ternary-based oxide deposition film formed onthe surface of the iron powder of the present invention and comprisingultra-fine grained metallic Fe particles dispersed in the matrix has afilm-thickness in a range from 5 to 500 nm so as to ensure high magneticflux density and high resistivity of the composite soft magneticmaterial formed by compacting the powder. Where the film thickness issmaller than 5 nm, it is not preferable, since the resistivity is notsufficient and eddy current loss is increased in the composite softmagnetic material formed by compacting the powder. On the other hand,where the film thickness is larger than 500 nm, it is not preferablesince the magnetic flux density is decreased in the composite softmagnetic material formed by compacting the powder. More preferably, thefilm thickness is in a range from 5 to 200 nm.

The Mg—Fe—O ternary-based oxide film formed on the surface of thepreviously invented Mg-containing iron oxide film-coated iron powder asdescribed in the above (f) to (k) has a sulfur-enriched layer at theboundary portion between the iron powder and the Mg—Fe—O ternary-basedoxide film comprising fine metallic Fe particles dispersed in thematrix, where the sulfur concentration of the sulfur-enriched layer ishigher than that of sulfur contained in a central portion of the ironpowder. The presence of the sulfur-enriched layer may be confirmed byperforming analysis of the sulfur concentration by Auger electronspectroscopy, showing the results of the analysis, where a peak of thesulfur concentration is shown in the graph. By the presence of such asulfur-enriched layer at the boundary portion, the Mg—Fe—O ternary-basedoxide film comprising ultra-fine grained metallic Fe particles dispersedin the matrix has further improved bonding to the surface of ironpowder, breakdown of the deposition film is prevented by tracking of thedeposition film to deformation of the powder at the time of compactingthe powder. High resistance is maintained by preventing contact andbonding of iron powder particles with each other at the time of heattreatment, high resistance is maintained, and therefore eddy currentloss is reduced. The iron powder contains sulfur as unavoidableimpurities. It is considered that most of the sulfur in thesulfur-enriched layer is provided by the sulfur contained in the surfaceportion of the iron powder.

It is preferable that the grain size of crystals constituting theMg—Fe—O ternary-based oxide deposition film formed on the surface of theMg-containing iron oxide film-coated iron powder of the above (f) to (k)is as small as possible. Preferably, the deposition film has a finecrystalline texture having a grain size of 200 nm or less. Because thefilm has such a fine crystalline texture, the fine crystalline Mg—Fe—Oternary-based oxide deposition film tracks the deformation of powderparticle at the time of compacting the powder, and is prevented frombreakdown. At the time of heat-treating, particles of the iron powder isprevented from being made to contact and bonded with each other. Whenthe powder is subjected to strain-relief heat treatment at hightemperature, because of the stable property of the oxide, reduction ofinsulation is prevented, high resistance is maintained, and eddy currentloss is lowered. Where the grain size is larger than 200 nm, it is notpreferable, because the film thickness of the Mg—Fe—O ternary-basedoxide deposition film exceeds 500 nm, and magnetic flux density ofcompacted composite soft magnetic material is reduced.

The MgO content in the outermost surface of the Mg—Fe—O ternary-basedoxide deposition film formed on the surface of the Mg-containing ironoxide film-coated iron powder of the above (k) is preferably as high aspossible. It is most preferable that the outermost surface issubstantially composed of MgO. Where the outermost surface issubstantially MgO, diffusion of Fe is inhibited at the time of heattreatment of the press-molded compact, the iron powder particles areprevented from contacting and bonding with each other, reduction ofinsulation is prevented, high resistance is ensured, and eddy currentloss is lowered.

An object of the present invention is to provide a composite softmagnetic powder produced by further coating MgO—SiO₂ composite oxidefilm having a MgO/SiO₂ value in a range from 1.0 to 3.0 in molar ratioon the surface of the previously invented Mg-containing iron oxidefilm-coated iron powder as described in (f) to (k). That is, the presentinvention has the following aspects.

(54) A composite soft magnetic powder comprising: Mg-containing ironoxide film-coated iron powder particles having iron powder particles,and Mg—Fe—O ternary-based oxide deposition films which disperse fine Fegrains in the matrices and are coated on surfaces of the iron powderparticles; and MgO—SiO₂ composite oxide films which have a MgO/SiO₂value in a range from 1.0 to 3.0 in molar ratio and are further coatedon surfaces of the Mg-containing iron oxide film-coated iron powderparticles.(55) A composite soft magnetic powder comprising: Mg-containing oxidefilm-coated iron powder particles having iron powder particles andMg—Fe—O ternary-based oxide deposition films coated on surfaces of theiron powder particles; and MgO—SiO₂ composite oxide films which have aMgO/SiO₂ value in a range from 1.0 to 3.0 in molar ratio and are coatedon surfaces of the Mg-containing oxide film-coated iron powderparticles, wherein the Mg—Fe—O ternary-based oxide deposition filmsinclude fine metallic Fe grains dispersed in the matrices and have aconcentration gradient where Mg and O decrease from exterior surfacestowards the interior direction, and Fe increases towards the interiordirection.(56) A composite soft magnetic powder as described in the above (54) or(55), wherein the Mg-containing oxide film-coated iron powder particlesfurther comprise sulfur-enriched layers in boundary portions between theiron powder particles and the Mg—Fe—O ternary-based oxide depositionfilms, where the sulfur-enriched layers contain higher concentrations ofsulfur than that contained in central portions of the iron powderparticles.(57) A composite soft magnetic powder as described in the above (54),(55), or (56), wherein the Mg—Fe—O ternary-based oxide deposition filmsdispersing ultra-fine grained metallic Fe grains in the matrix have acrystalline MgO-dissolving wustite phase in the matrices.(58) A Mg-containing oxide film-coated iron powder as described in theabove (54), (55), (56), or (57), wherein the above-described Mg—Fe—Oternary-based oxide deposition films have microcrystalline structureshaving a grain size of 200 nm or less.(59) A Mg-containing oxide film-coated iron powder as described in theabove (54), (55), (56), (57) or (58), wherein the outermost surfaces ofthe above-described Mg—Fe—O ternary-based oxide deposition films aresubstantially composed of MgO.

The composite soft magnetic powder of the present invention as describedin the above (54), (55), (56), (57), (58) and (59) may be produced by:preparing a mixed oxide sol-solution of MgO and SiO₂ obtained by mixing,in volumetric ratio, alkoxysilane solution:1 and magnesium-alkoxidesolution:1 to 3; adhering the sol-solution to the surface of theMg-containing iron oxide film-coated iron powder as described in theabove (f), (g), (h), (i), (j), or (k); and heating and drying thepowder.

(60) A composite soft magnetic material constituted of an iron particlephase and grain boundary phase surrounding the iron particle phase,where the grain boundary phase contains Mg—Fe—O ternary-based oxideincluding crystalline MgO-dissolving wustite phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a result of Auger electron spectroscopicanalysis of sulfur distribution in the thickness direction of a Mg—Fe—Oternary-based oxide deposition film at least containing (Mg, Fe)O.

FIG. 2 is a graph showing a result of Auger electron spectroscopicanalysis of distribution of Mg, O, and Fe concentrations in thicknessdirection of a Mg—Fe—O ternary-based oxide deposition film having finemetallic Fe particles dispersed in the matrix.

FIG. 3 is a graph showing a result of Auger electron spectroscopicanalysis of sulfur distribution in the thickness direction of a Mg—Fe—Oternary-based oxide deposition film having fine metallic Fe particlesdispersed in the matrix.

FIG. 4 is a electron microscopic image showing a texture of a section ofa Mg—Fe—O ternary-based oxide deposition film having fine metallic Feparticles dispersed in the matrix.

FIG. 5 is a transmission electron microscopic image of a texture of asection of a deposition film formed in the deposition film-coated ironpowder of the present invention.

FIG. 6 is a graph showing a result of Auger electron spectroscopicanalysis of distribution of Mg, O, P, and Fe concentrations in thicknessdirection of a deposition film formed in the deposition film-coated ironpowder of the present invention.

FIG. 7 is a graph showing a result of Auger electron spectroscopicanalysis of distribution of Mg, Si, O, and Fe concentrations inthickness direction of an oxide deposition film.

FIG. 8 is a graph showing a result of Auger electron spectroscopicanalysis of distribution of Mg, Si, O, and Fe concentrations inthickness direction of an oxide deposition film.

BEST MODE FOR CARRYING OUT THE INVENTION Example 1

As a stock powder (raw powder material), pure iron powder having a meangrain size of 70 μm and including a trace amount of sulfur as anunavoidable impurity was prepared. In addition, Mg powder having a meangrain size of 50 μm was prepared. Oxidation-treated iron powder havingan iron oxide film on the surface was produced by performing oxidizationtreatment of the pure iron powder by heating the iron powder at atemperature of 220° C. for 2 hours in air. A mixed powder was producedby adding the prepared Mg powder to the oxidation-treated iron powder ina proportion of oxidation-treated iron powder: Mg powder=99.8 mass %:0.2 mass %, and mixing the powder. The obtained mixed powder wasretained at a temperature of 650° C. under a pressure of 2.7×10⁻⁴ MPafor 1 hour, and further retained at a temperature of 200° C. for 1 hourin air. Thus, Mg-containing oxide film-coated iron powder 1 of thepresent invention having a coating of deposition film on the surface ofiron powder was produced. The texture of the deposition film formed onthe Mg-containing oxide film-coated iron powder 1 of the presentinvention was observed using a transmission electron microscope and athickness and maximum grain size of the deposition film were determined.The results are shown in Table 1. In addition, electron beam diffractionpatterns obtained from the Mg-containing oxide film-coated iron powder 1of the present invention showed the presence of a MgO-dissolving wustitephase in the film.

By the analysis of bonding energies by analyzing the deposition filmformed on the surface of Mg-containing oxide film-coated iron powder 1of the present invention using an X-ray photoelectron spectrometer, itwas confirmed that the deposition film was a Mg—Fe—O ternary-based oxidedeposition film at least containing (Mg, Fe)O. In addition, boundaryportion between the iron powder and the Mg—Fe—O ternary-based oxidedeposition film was examined by a method using an Auger electronspectrometer, and the results are shown in the graph of FIG. 1.

In the graph of FIG. 1, the vertical axis denotes a peak intensity ofAuger electron, and the horizontal axis denotes time of etching thecoating deposition film. A long etching time denotes a deep position inthe coating deposition film. In FIG. 1, the graph of sulfurconcentration detected by Auger electron spectroscopy shows a peak ofthe sulfur concentration. In this graph, a sulfur peak of Auger electronspectrum obviously higher than the background constituted of impuritysulfur contained in the central portion of iron powder was obviouslydetected in the boundary portion between the deposition film and ironpowder, where the boundary portion corresponded to etching time of 10 to15 minutes. Thus, from the observation of this graph, the presence of asulfur-enriched layer containing a higher concentration of sulfur thanthat of the core portion of iron powder was confirmed in the boundaryportion between the deposition film and iron powder.

Example 2

Oxidation-treated iron powder having an iron oxide film on the surfacewas produced by oxidizing the pure iron powder prepared in Example 1 byretaining at a temperature of 210° C. for 3 hours in air. Compared withExample 1, a larger amount of Mg powder was added to, and mixed with theoxidation-treated iron powder, and a mixed powder having a proportion ofoxidation treated iron powder: Mg powder=99.5 mass %:0.5 mass % wasprepared. The obtained mixed powder was retained for 1 hour at atemperature of 670° C. under a pressure of 1×10⁻⁵ MPa, and furtherretained for 1 hour at a temperature of 200° C. in air. Thus theMg-containing oxide-film coated iron powder 2 comprising iron powderhaving a surface coating of a deposition film was produced. The textureof the deposition film formed on the Mg-containing oxide film-coatediron powder 2 of the present invention was observed using a transmissionelectron microscope and a thickness and maximum grain size of thedeposition film were determined. The results are shown in Table 1. Inaddition, from electron beam diffraction patterns obtained from thedeposition film, it was confirmed that the film contained crystallineMgO-dissolving wustite.

By the analysis of bonding energies by analyzing the deposition filmformed on the surface of Mg-containing oxide film-coated iron powder 2of the present invention using an X-ray photoelectron spectrometer, itwas confirmed that the deposition film was a Mg—Fe—O ternary-based oxidedeposition film at least containing (Mg, Fe)O, and the outermost surfaceof the Mg—Fe—O ternary-based oxide deposition film was composed of MgO.In addition, in the same manner as in Example 1, concentrationdistributions of Mg, Fe, and O were examined using an Auger electronspectroscopic analyzer. As a result, the presence of a sulfur-enrichedlayer containing a higher concentration of sulfur than that of the coreportion of iron powder was confirmed in the boundary portion between thedeposition film and iron powder.

Example 3

Oxidation-treated iron powder having an iron oxide film on the surfacewas produced by oxidizing the pure iron powder prepared in Example 1 byretaining at a temperature of 220° C. for 1.5 hours in air. Comparedwith Example 1, a larger amount of Mg powder was added to, and mixedwith the oxidation-treated iron powder, and a mixed powder having aproportion of oxidation treated iron powder: Mg powder=99.7 mass %: 0.3mass % was prepared. The obtained mixed powder was retained for 1 hourat a temperature of 640° C. under a pressure of 1×10⁻⁴ MPa, and furtherretained for 1.5 hour at a temperature of 200° C. in air. Thus, theMg-containing oxide-film coated iron powder 3 of the present inventioncomprising iron powder having a surface coating of a deposition film wasproduced. The texture of the deposition film was observed using atransmission electron microscope and a thickness and maximum grain sizeof the deposition film were determined. The results are shown in Table1.

By the analysis of bonding energies by analyzing the deposition filmformed on the surface of Mg-containing oxide film-coated iron powder 3of the present invention using an X-ray photoelectron spectrometer, itwas confirmed that the deposition film was a Mg—Fe—O ternary-based oxidedeposition film at least containing (Mg, Fe)O, and the outermost surfaceof the Mg—Fe—O ternary-based oxide deposition film was composed of MgO.In addition, in the same manner as in Example 1, concentrationdistributions of Mg, Fe, and O were examined using an Auger electronspectroscopic analyzer. As a result, the presence of a sulfur-enrichedlayer containing a higher concentration of sulfur than that of the coreportion of iron powder was confirmed in the boundary portion between theMg—Fe—O ternary-based oxide deposition film and iron powder.

The Mg-containing oxide film-coated iron powders 1-3 of the presentinvention obtained in Examples 1 to 3 were charged in moulds, and werepress-molded into compacts, thereby plate-shaped compacts each having adimension of length: 55 mm, width: 10 mm, and thickness: 5 mm, andring-shaped compacts each having a dimension of external diameter: 35mm, internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of a nitrogen atmosphere,temperature: 500° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magneticmaterials constituted of the plate shaped heat-treated articles weresubjected to measurements of resistivity, and the results are shown inTable.1. Windings were formed on the composite soft magnetic materialsconstituted of the ring-shaped heat-treated article, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 1.5 T and frequency of 50 Hz, and core loss under conditionsof magnetic flux density of 1.0 T and frequency of 400 Hz were measured.The results are shown in Table 1. In addition, the composite softmagnetic material utilizing the Mg-containing oxide film-coated ironpowder 2 of the present invention obtained in Example 2 was observedusing a transmission electron microscope. As a result, an iron particlephase and grain boundary phase surrounding the iron particle phase wereobserved. From the electron beam diffraction pattern obtained from thegrain boundary phase, it was confirmed that the grain boundary phasecontained Mg—Fe—O ternary-based oxides including crystallineMgO-dissolving wustite.

Conventional Example 1

Conventional oxide-coated iron powder 1 was produced by chemicallyforming Mg-containing ferrite layer on the surface of the pure ironpowder prepared in Example 1. The conventional oxide-coated iron powderwas charged in moulds, and was press-molded into compacts, thereby aplate-shaped compact having a dimension of length: 55 mm, width: 10 mm,and thickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were heat-treated under conditions ofa nitrogen atmosphere, temperature: 500° C., and retention time: 30minutes. Thus, composite soft magnetic materials constituted of aplate-shaped or ring-shaped heat-treated article were produced. Theplate-shaped composite soft magnetic material was subjected tomeasurement of resistivity, and the result is shown in Table.1. Windingwas formed on the composite soft magnetic material constituted of thering-shaped heat-treated article, and magnetic flux density, coerciveforce, core loss under conditions of magnetic flux density of 1.5 T andfrequency of 50 Hz, and core loss under conditions of magnetic fluxdensity of 1.0 T and frequency of 400 Hz were measured. The results areshown in Table 1.

TABLE 1 THE PRESENT OXIDE-COATED INVENTION CONVEN- IRON POWDER 1 2 3TIONAL 1 Mg—Fe—O Thickness 40 100 50 — ternary- (nm) based oxide Maximum20 70 30 — deposition grain size film Concentration present presentpresent — containing gradient (Mg,Fe)O of Mg, Fe, O Sulfur-enrichedpresent present present — layer in boundary portion MgO in the absentpresent present — outermost surface Properties of Density 7.67 7.64 7.667.65 composite (g/cm³) soft Flux density 1.69 1.66 1.68 1.60 magneticB_(10KA/m) (T) material Coercive force 190 185 190 220 (A/m) Core loss*8.0 8.0 7.9 60 (W/kg) Core loss** 47 47 45 800 (W/kg) Resistivity 110130 120 0.4 (μΩm) Core loss* denotes core loss at flux density of 1.5 Tand frequency of 50 Hz Core loss** denotes core loss at flux density of1.0 T and frequency of 400 Hz

From the result shown in Table 1, the following are understood. Wherecomposite soft magnetic materials produced using Mg-containing oxidefilm-coated iron powder 1-3 of the present invention are compared withthe conventional composite soft magnetic material produced usingconventional oxide-coated iron powder 1, no remarkable difference can beobserved in the density. On the other hand, compared to the conventionalcomposite soft magnetic material produced using conventionaloxide-coated iron powder 1, composite soft magnetic materials producedusing Mg-containing oxide film-coated iron powders 1-3 of the presentinvention have high magnetic flux density, low coercive force,remarkably high resistivity, and therefore have remarkably low core losswhich is especially low as the frequency increases. Therefore, it isunderstood that compared to the conventional oxide-coated iron powder 1,Mg-containing oxide film-coated powders 1 to 3 of the invention are softmagnetic raw material powders which can provide composite soft magneticmaterials having further excellent properties.

Example 4

As a stock powder, pure iron powder having a mean grain size of 70 μmand including a trace amount of sulfur as an unavoidable impurity wasprepared. In addition, Mg powder having a mean grain size of 50 μm wasprepared. Oxidation-treated iron powder having an iron oxide film on thesurface was produced by performing oxidization treatment of the pureiron powder by heating the iron powder at a temperature of 220° C. for 2hours in air. A mixed powder was produced by adding the prepared Mgpowder to the oxidation-treated iron powder in a proportion ofoxidation-treated iron powder: Mg powder=99.8 mass %: 0.2 mass %, andmixing the powder. The obtained mixed powder was retained at atemperature of 650° C. under a pressure of 1×10⁻⁴ MPa for 1 hour whilebeing rolled. Thus, Mg-containing oxide film-coated iron powder 4 of thepresent invention having a coating of deposition film on the surface ofiron powder was produced. The texture of the deposition film formed onthe Mg-containing oxide film-coated iron powder 4 of the presentinvention was observed using a transmission electron microscope and athickness and maximum grain size of the deposition film were determined.The results are shown in Table 2. FIG. 4 is a photograph of texturetaken in the observation of the sectional texture of the above-describeddeposition film using the transmission electron microscope. From FIG. 4,it can be understood that a deposition film of the present invention iscoated on the surface of the iron powder (upper right), and that thedeposition film has a thickness of 40 nm and maximum grain size of 20nm. In addition, electron beam diffraction patterns obtained from thedeposition film of the present invention showed the presence of aMgO-dissolving wustite phase in the film.

By the analysis of bonding energies by analyzing the deposition filmformed on the surface of Mg-containing oxide film-coated iron powder 4of the present invention using an X-ray photoelectron spectrometer, itwas confirmed that fine particles of metallic Fe were dispersed in thematrix. In addition, it was confirmed that the outermost surface of thedeposition film dispersing the fine metallic Fe particles in the matrixwas composed of MgO. In addition, concentration distributions of Mg, O,and Fe in depth direction of the deposition film were examined using anAuger electron spectroscopic analyzer, and the results are shown in FIG.2

The graph of FIG. 2 shows analytical results in depth direction of thedeposition film. In the graph of FIG. 2, the vertical axis denotes apeak intensity of Auger electron, and the horizontal axis denotes timeof etching the coating deposition film. A long etching time denotes adeep position in the coating deposition film. From FIG. 2, it can beunderstood that the film has concentration gradients of Mg and Odecreasing from the surface towards the interior direction, and has aconcentration gradient of Fe increasing towards the interior direction.Therefore, it can be understood that: the deposition film of theMg-containing oxide film-coated iron powder 4 of the present inventionis a Mg—Fe—O ternary-based oxide deposition film dispersing fine Feparticles in the matrix; the Mg—Fe—O ternary-based oxide deposition filmhas concentration gradients such that Mg and O decreases from thesurface towards the interior direction, and Fe increases towards theinterior direction; the deposition film includes crystallineMgO-dissolving wustite phase; and the outermost surface of thedeposition film was composed of MgO.

In addition, boundary portion between the iron powder and the Mg—Fe—Oternary-based oxide deposition film was examined by using an Augerelectron spectroscopic analyzer. The results are shown in the graph ofFIG. 3. In the graph of FIG. 3, the vertical axis denotes a peakintensity of Auger electron, and the horizontal axis denotes time ofetching the coating deposition film. As long an etching time denotes asdeep a position in the coating deposition film. In FIG. 1, the graph ofsulfur concentration detected by Auger electron spectroscopy shows apeak of the sulfur concentration. In this graph, a sulfur peak of Augerelectron spectrum obviously higher than the background constituted ofimpurity sulfur (background) contained in the central portion of ironpowder was obviously detected in the boundary portion between thedeposition film and iron powder, where the boundary portion correspondedto etching time of 10 to 15 minutes. Thus, from the observation of thisgraph, the presence of a sulfur-enriched layer containing a higherconcentration of sulfur than that of the core portion of iron powder wasconfirmed in the boundary portion between the deposition film and ironpowder.

Example 5

Oxidation-treated iron powder having an iron oxide film on the surfacewas produced by oxidizing the pure iron powder prepared in Example 4 byretaining the powder at a temperature of 215° C. for 3 hours in air.Compared with Example 4, a larger amount of Mg powder was added to, andmixed with the oxidation-treated iron powder, and a mixed powder havinga proportion of oxidation treated iron powder: Mg powder=99.5 mass %:0.5 mass % was prepared. By retaining the obtained mixed powder for 1hour at a temperature of 660° C. under a pressure of 1×10⁻⁴ MPa whiletumbling the mixed powder, Mg-containing oxide-film coated iron powder 5of the invention comprising iron powder having a surface coating of adeposition film was produced.

Texture of a section of the deposition film formed on the Mg-containingoxide film-coated iron powder 5 of the present invention was observedusing a transmission electron microscope and a thickness and maximumgrain size of the deposition film were determined. The results are shownin Table 2. In addition, from electron beam diffraction patternsobtained from the deposition film, it was confirmed that the filmcontained crystalline MgO-dissolving wustite phase.

By the analysis of bonding energies by analyzing the deposition filmformed on the surface of Mg-containing oxide film-coated iron powder 5of the present invention using an X-ray photoelectron spectrometer, itwas confirmed that fine metallic iron particles were dispersed in thematrix of the deposition film, the deposition film includedMgO-dissolving wustite phase, and the outermost surface of thedeposition film was composed of MgO. Therefore, it can be understoodthat: the deposition is a Mg—Fe—O ternary-based oxide deposition filmdispersing fine Fe particles in the matrix; the deposition film includescrystalline MgO-dissolving wustite phase; and the outermost surface ofthe deposition film was composed of MgO.

In addition, in the same manner as in Example 4, concentrationdistributions of Mg, Fe, and O were examined using an Auger electronspectroscopic analyzer. As a result, it was confirmed that thedeposition film had concentration gradients such that Mg and O decreasedfrom the surface towards the interior direction, and Fe increasedtowards the interior direction and that a sulfur-enriched layercontaining a higher concentration of sulfur than that of the coreportion of iron powder was present in the boundary portion between theiron powder and the Mg—Fe—O ternary-based oxide deposition film.

Example 6

Oxidation-treated iron powder having an iron oxide film on the surfacewas produced by oxidizing the pure iron powder prepared in Example 4 byretaining at a temperature of 220° C. for 2.0 hours in air. Comparedwith Example 4, a larger amount of Mg powder was added to, and mixedwith the oxidation-treated iron powder, and a mixed powder having aproportion of oxidation treated iron powder: Mg powder=99.7 mass %: 0.3mass % was prepared. By retaining the obtained mixed powder for 1 hourat a temperature of 640° C. under a pressure of 1×10⁻⁵ MPa whiletumbling the mixed powder, Mg-containing oxide-film coated iron powder 6of the present invention comprising iron powder having a surface coatingof a deposition film was produced. The texture of the deposition filmwas observed using a transmission electron microscope and a thicknessand maximum grain size of the deposition film were determined. Theresults are shown in Table 2. In addition, from the electron beamdiffraction pattern obtained from the deposition film, it was confirmedthat the film included crystalline MgO-dissolving wustite phase.

In the analysis of the deposition film formed on the surface ofMg-containing oxide film-coated iron powder 6 of the present inventionusing an X-ray photoelectron spectrometer, from the bonding energies, itwas confirmed that at least fine metallic Fe particles were dispersed inthe matrix of the deposition film, the deposition film included MgOdissolving wustite phase, and that the outermost surface of the Mg—Fe—Oternary-based oxide deposition film was composed of MgO. Therefore, itcan be understood that the deposition film of the Mg-containing oxidefilm-coated iron powder 6 of the present invention is a Mg—Fe—Oternary-based oxide deposition film, the deposition film includescrystalline MgO-dissolving wustite phase, and the outermost surface ofthe deposition film is composed of MgO.

In addition, in the same manner as in Example 4, concentrationdistributions of Mg, O, and Fe of the deposition film was examined usingan Auger electron spectroscopic analyzer. As a result, it was confirmedthat: the deposition film had concentration gradients such that Mg and Odecreased from the surface towards the interior direction, and Feincreased towards the interior direction; and that a sulfur-enrichedlayer containing a higher concentration of sulfur than that of the coreportion of iron powder was present in the boundary portion between theiron powder and the Mg—Fe—O ternary-based oxide deposition film.

The Mg-containing oxide film-coated iron powders 4-6 of the presentinvention obtained in Examples 4 to 6 were charged in moulds, and werepress-molded into compacts, thereby plate-shaped compacts each having adimension of length: 55 mm, width: 10 mm, and thickness: 5 mm, andring-shaped compacts each having a dimension of external diameter: 35mm, internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of a nitrogen atmosphere,temperature: 500° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The plate-shaped composite softmagnetic materials were subjected to measurements of resistivity, andthe results are shown in Table.2. Windings were formed on the compositesoft magnetic materials constituted of the ring-shaped heat-treatedarticle, and magnetic flux density, coercive force, core loss underconditions of magnetic flux density of 1.5 T and frequency of 50 Hz, andcore loss under conditions of magnetic flux density of 1.0 T andfrequency of 400 Hz were measured. The results are shown in Table 2. Inaddition, composite soft magnetic materials utilizing the Mg-containingoxide film coated iron powder 4 to 6 of the present invention obtainedin Example 4 to 6 were observed using a transmission electronmicroscope. As a result, iron particle phase originated from the ironpowder and grain boundary phase surrounding the iron particle phase wereobserved in each of the composite soft magnetic materials. From theelectron beam diffraction patterns obtained from the grain boundaryphases, it was confirmed that the grain boundary phases containedMg—Fe—O ternary-based oxides including crystalline MgO-dissolvingwustite phase.

Conventional Example 2

Conventional oxide-coated iron powder 2 was produced by chemicallyforming Mg-containing ferrite layer on the surface of the pure ironpowder prepared in Example 4. The conventional oxide-coated iron powder2 was charged in moulds, and was press-molded into compacts, thereby aplate-shaped compact having a dimension of length: 55 mm, width: 10 mm,and thickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were heat-treated under conditions ofa nitrogen atmosphere, temperature: 500° C., and retention time: 30minutes. Thus, composite soft magnetic materials constituted of aplate-shaped or ring-shaped heat-treated article were produced. Thecomposite soft magnetic material constituted of the plate-shapedheat-treated article was subjected to measurement of resistivity, andthe result is shown in Table.2. Winding was formed on the composite softmagnetic material constituted of the ring-shaped heat-treated article,and magnetic flux density, coercive force, core loss under conditions ofmagnetic flux density of 1.5 T and frequency of 50 Hz, and core lossunder conditions of magnetic flux density of 1.0 T and frequency of 400Hz were measured. The results are shown in Table 2.

TABLE 2 THE PRESENT OXIDE-COATED INVENTION CONVEN- IRON POWDER 4 5 6TIONAL 1 Mg—Fe—O Thickness 40 110 60 — ternary- (nm) based oxide Maximum20 80 30 — deposition grain size film Concentration present presentpresent — dispersing gradient of ultra-fine Mg, Fe, O metallic FeSulfur-enriched present present present — particles layer in boundaryportion MgO in the present present present — outermost surfaceProperties of Density 7.68 7.65 7.67 7.65 composite (g/cm³) soft Fluxdensity 1.70 1.67 1.70 1.60 magnetic B_(10KA/m) (T) material Coerciveforce 185 180 185 220 (A/m) Core loss* 8.1 8.0 8.0 60 (W/kg) Core loss**49 48 47 800 (W/kg) Resistivity 105 120 115 0.4 (μΩm) Core loss* denotescore loss at flux density of 1.5 T and frequency of 50 Hz Core loss**denotes core loss at flux density of 1.0 T and frequency of 400 Hz

From the results shown in Table 2, the following are understood Wherecomposite soft magnetic materials produced using Mg-containing oxidefilm-coated iron powders 4-6 of the present invention are compared withthe conventional composite soft magnetic material produced usingconventional oxide-coated iron powder 2, no remarkable difference can beobserved in the density. On the other hand, compared to the conventionalcomposite soft magnetic material produced using conventionaloxide-coated iron powder 2, composite soft magnetic materials producedusing Mg-containing oxide film-coated iron powders 4-6 of the presentinvention have high magnetic flux density, low coercive force,remarkably high resistivity, and therefore has remarkably low core losswhich is especially low as the frequency increase. Therefore, it isunderstood that, compared to the conventional oxide-coated iron powder2, Mg-containing oxide film-coated powders 4 to 6 of the invention aresoft magnetic raw material powders which can provide composite softmagnetic materials having further excellent properties.

Example 7

As a stock powder, commercially available sulfate-coated iron powderhaving a mean grain size of 70 μm, and Mg powder having a mean grainsize of 50 μm were prepared. A mixed powder was produced by adding theMg powder to the sulfate-coated iron powder in such a proportion thatthe sulfate-coated iron powder: Mg powder=99.8 mass %: 0.2 mass %, andmixing the powder. By retaining the obtained mixed powder at atemperature of 650° C. under a pressure of 1×10⁻⁴ MPa for 1 hour whiletumbling the powder, deposition film-coated iron powder of the presentinvention comprising iron powder and a deposition film coated on thesurface of the iron powder was produced. Texture of a section of thedeposition film formed on the deposition film-coated iron powder of thepresent invention was observed using a transmission electron microscope,and electron micrograph of the texture was shown in FIG. 5. From thephotograph of FIG. 5, thickness and maximum grain size of the depositionfilm formed on the deposition film-coated iron powder of the presentinvention were determined. The results are shown in Table 3.

The graph of FIG. 6 shows analytical results of concentration gradientof Mg, Fe, O, and P in depth direction of the deposition film. From theresults shown in the graph of FIG. 6, it was confirmed that elementsconstituting the deposition film were Mg, Fe, P and O.

The deposition film formed on the deposition film-coated iron powder ofthe present invention was analyzed using an X-ray photoelectronspectrometer. From the results of analysis of bonding energies, it wasconfirmed that fine particles of iron phosphide were dispersed in thematrix and that Mg—Fe—P—O quaternary-based phosphate comprising Mg, Fe,P, and O, and Mg—Fe—O ternary-based oxide comprising Mg, Fe, and O werepresent in the film. Further, from the electron beam diffraction patternof the deposition film formed on the surface of the depositionfilm-coated iron powder of the present invention, it was confirmed thatthe Mg—Fe—P—O quaternary-based phosphate comprising Mg, Fe, P, and O,and Mg—Fe—O ternary-based oxide comprising Mg, Fe, and O includedcrystalline MgO-dissolving wustite type phase.

The obtained deposition film-coated iron powder of the present inventionwas charged in moulds, and was press-molded into compacts, thereby aplate-shaped compact having a dimension of length: 55 mm, width: 10 mm,and thickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were heat-treated under conditions ofa nitrogen atmosphere, temperature: 500° C., and retention time: 30minutes. Thus, composite soft magnetic materials constituted of aplate-shaped or ring-shaped heat-treated article were produced. Theplate-shaped composite soft magnetic material was subjected tomeasurement of density and resistivity, and the results are shown inTable.3. Winding was formed on the composite soft magnetic materialconstituted of the ring-shaped heat-treated article, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 1.5 T and frequency of 50 Hz, and core loss under conditionsof magnetic flux density of 1.0 T and frequency of 400 Hz were measured.The results are shown in Table 3.

In addition, composite soft magnetic materials utilizing the depositionfilm-coated iron powder of the present invention were observed using atransmission electron microscope. As a result, iron particle phase andgrain boundary phase surrounding the iron particle phase were observed.From the electron beam diffraction pattern obtained from the grainboundary phase, it was confirmed that the grain boundary phase includedcrystalline MgO-dissolving wustite phase.

Conventional Example 3

Conventional oxide-coated iron powder was produced by chemically formingMg-containing ferrite layer on the surface of pure iron powder. Theconventional oxide-coated iron powder was charged in moulds, and waspress-molded into compacts, thereby a plate-shaped compact having adimension of length: 55 mm, width: 10 mm, and thickness: 5 mm, and aring-shaped compact having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of a nitrogen atmosphere,temperature: 500° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magnetic materialconstituted of the plate-shaped heat-treated article was subjected tomeasurement of resistivity, and the result is shown in Table.3. Windingwas formed on the composite soft magnetic material constituted of thering-shaped heat-treated article, and magnetic flux density, coerciveforce, core loss under conditions of magnetic flux density of 1.5 T andfrequency of 50 Hz, and core loss under conditions of magnetic fluxdensity of 1.0 T and frequency of 400 Hz were measured. The results areshown in Table 3.

TABLE 3 DEPOSITION FILM-COATED IRON CONVENTIONAL POWDER OF THE OXIDEFILM-COATED TYPE INVENTION IRON POWDER Deposition Thickness (nm) 60 —film Maximum 20 — grain size Properties of Density (g/cm3) 7.69 7.65composite Flux density 1.72 1.60 soft magnetic B10KA/m (T) materialCoercive force 170 210 (A/m) Core loss* (W/kg) 7.8 60 Core loss** (W/kg)49 800 Resistivity 50 0.4 (μΩm) Core loss* denotes core loss at fluxdensity of 1.5 T and frequency of 50 Hz Core loss** denotes core loss atflux density of 1.0 T and frequency of 400 Hz

From the result shown in Table 3, the following are understood. Wherecomposite soft magnetic materials produced using the depositionfilm-coated iron powder of the present invention are compared with theconventional composite soft magnetic material produced usingconventional oxide-coated iron powder, no remarkable difference can beobserved in the density. On the other hand, compared to the conventionalcomposite soft magnetic material produced using conventionaloxide-coated iron powder, composite soft magnetic materials producedusing the deposition film-coated iron powder of the present inventionhave high magnetic flux density, low coercive force, remarkably highresistivity, and therefore has remarkably low core loss which isespecially low as the frequency increase. Therefore, it is understoodthat, compared to the conventional oxide-coated iron powder, thedeposition film-coated powder of the invention is soft magnetic rawmaterial powder which can provide composite soft magnetic materialshaving further excellent properties.

Example 8

As a stock powder, gas-water-atomized iron silicide powder having acomposition containing Si:3 mass % and the balance consisting of Fe andunavoidable impurities, and having a mean grain size of 70 μm wasprepared. In addition, Mg powder having a mean grain size of 50 μm wasprepared.

An oxide film was formed on the surface of the gas-water-atomized ironsilicide powder. A mixed powder was produced by adding the Mg powder tothe iron silicide powder in such a proportion that the iron silicidepowder: Mg powder=99.8 mass %: 0.2 mass %, and mixing the powder. Theobtained mixed powder was retained at a temperature of 650° C. under apressure of 2.7×10⁻⁴ MPa for 1 hour, and was further retained at atemperature of 200° C. for 1 hour in air. Thus, depositionoxide-film-coated iron silicide powder of the invention comprising ironsilicide powder and oxide deposition film formed on the surface of theiron silicide powder was produced.

Concentration distributions of Mg, Si, and O in depth direction of thedeposition film of the deposition film-coated iron silicide powder wereexamined using an Auger electron spectroscopic analyzer. The results areshown in FIG. 7. The graph of FIG. 7 shows analytical results in depthdirection of the deposition film. In the graph of FIG. 7, the verticalaxis denotes a peak intensity of Auger electron, and the horizontal axisdenotes time of etching the deposition film. As long an etching timedenotes as deep a position in the deposition film. From FIG. 7, it isunderstood that the deposition film has concentration gradients where Mgand O decreases from the surface towards the interior direction, Feincreases towards the interior direction, and Si content increases inthe vicinity of the outermost surface such that a portion close to theoutermost surface shows as a high Si content.

In addition, the deposition film formed on the surface of thedeposition-film coated iron silicide powder was analyzed using a X-rayphotoelectron spectroscopic analyzer, and bonding energies wereexamined. As a result, it was confirmed that metallic Fe or Fe—Si alloywere included in the deposition film.

From the electron beam diffraction pattern of the deposition film formedon the surface of the deposition-film coated iron silicide powder of thepresent invention, it was confirmed that the Mg—Si—Fe—O quaternary-basedoxide deposition film included MgO-dissolving wustite type phase.

Therefore, the followings can be understood. The deposition oxide filmformed on the surface of the deposition-film coated iron silicide powderof the present invention is a Mg—Si—Fe—O quaternary-based oxidedeposition film comprising Mg, Si, Fe, and O. The Mg—Si—Fe—Oquaternary-based oxide deposition film of the present invention hasconcentration gradients where Mg and O decreases from the surfacetowards the interior direction, Fe increases towards the interiordirection, and has a concentration gradient of Si where Si contentincreases in the vicinity of the outermost surface such that a portionclose to the outermost surface shows as a high Si content. Metallic Feor Fe—Si alloy is contained. The Mg—Si—Fe—O quaternary-based oxidedeposition film includes crystalline MgO-dissolving wustite-type phase.In addition, the texture of the deposition film in the depositionfilm-coated iron silicide powder was observed using a transmissionelectron microscope, and thickness and maximum grain size of the oxidedeposition film were measured. As a result, the oxide deposition filmhad an average thickness of 40 nm and maximum grain size of 10 nm.

The obtained oxide deposition film-coated iron silicide powder of thepresent invention was charged in moulds, and was press-molded intocompacts, thereby a plate-shaped compact having a dimension of length:55 mm, width: 10 mm, and thickness: 5 mm, and a ring-shaped compacthaving a dimension of external diameter: 35 mm, internal diameter: 25mm, and height: 5 mm were formed. The obtained compacts wereheat-treated under conditions of a nitrogen atmosphere, temperature:600° C., and retention time: 30 minutes. Thus, composite soft magneticmaterials constituted of a plate-shaped or ring-shaped heat-treatedarticle were produced. The plate-shaped composite soft magnetic materialwas subjected to measurement of resistivity, and the result is shown inTable.4. Winding was formed on the composite soft magnetic materialconstituted of the ring-shaped heat-treated article, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 0.1 T and frequency of 10 kHz, and core loss under conditionsof magnetic flux density of 1.0 T and frequency of 400 Hz were measured.The results are shown in Table 4. In addition, composite soft magneticmaterials utilizing the oxide deposition film-coated iron silicidepowder of the present invention were observed using a transmissionelectron microscope. As a result, iron particle phase and grain boundaryphase surrounding the iron particle phase were observed. From theelectron beam diffraction pattern obtained from the grain boundaryphase, it was confirmed that the grain boundary phase includedcrystalline MgO-dissolving wustite type phase.

Conventional Example 4

Conventional conversion treatment film-coated iron silicide powder wasproduced by chemically forming Mg-containing conversion treatment filmon the surface of the iron silicide powder prepared in Example 8. Theconventional conversion treatment film-coated iron silicide powder wascharged in moulds, and was press-molded into compacts, thereby aplate-shaped compact having a dimension of length: 55 mm, width: 10 mm,and thickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were heat-treated under conditions ofa nitrogen atmosphere, temperature: 600° C., and retention time: 30minutes. Thus, composite soft magnetic materials constituted of aplate-shaped or ring-shaped heat-treated article were produced. Thecomposite soft magnetic material constituted of the plate-shapedheat-treated article was subjected to measurement of resistivity, andthe result is shown in Table.4. Winding was formed on the composite softmagnetic material constituted of the ring-shaped heat-treated article,and magnetic flux density, coercive force, core loss under conditions ofmagnetic flux density of 0.1 T and frequency of 10 kHz, and core lossunder conditions of magnetic flux density of 1.0 T and frequency of 400Hz were measured. The results are shown in Table 4.

Example 9

Silicone resin in an amount of 1 mass % was added to, and mixed with theoxide deposition film-coated iron silicide powder of the presentinvention produced in Example 8. The obtained mixed powder was chargedin moulds, and was press-molded into compacts, thereby a plate-shapedcompact having a dimension of length: 55 mm, width: 10 mm, andthickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were heat-treated under conditions ofvacuum atmosphere, temperature: 800° C., and retention time: 30 minutes.Thus, composite soft magnetic materials constituted of a plate-shaped orring-shaped heat-treated article were produced. The composite softmagnetic material constituted of the plate-shaped heat-treated articlewas subjected to measurement of resistivity, and the result is shown inTable.4. Winding was formed on the composite soft magnetic materialconstituted of the ring-shaped heat-treated article, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 0.1 T and frequency of 10 kHz, and core loss under conditionsof magnetic flux density of 1.0 T and frequency of 400 Hz were measured.The results are shown in Table 4. In addition, composite soft magneticmaterials were observed using a transmission electron microscope. As aresult, iron particle phase and grain boundary phase surrounding theiron particle phase were observed. From the electron beam diffractionpattern obtained from the grain boundary phase, it was confirmed thatthe grain boundary phase included crystalline MgO-dissolving wustitetype phase.

Conventional Example 5

Silicone resin in an amount of 1 mass % was added to, and mixed with theconventional conversion treatment film-coated iron silicide powderproduced in Conventional Example 4 by chemically forming Mg-containingconversion treatment film on the surface of the iron silicide powder.The obtained mixed powder was charged in moulds, and was press-moldedinto compacts, thereby a plate-shaped compact having a dimension oflength: 55 mm, width: 10 mm, and thickness: 5 mm, and a ring-shapedcompact having a dimension of external diameter: 35 mm, internaldiameter: 25 mm, and height: 5 mm were formed. The obtained compactswere heat-treated under conditions of vacuum atmosphere, temperature:800° C., and retention time: 30 minutes. Thus, composite soft magneticmaterials constituted of a plate-shaped or ring-shaped heat-treatedarticle were produced. The composite soft magnetic material constitutedof the plate-shaped heat-treated article was subjected to measurement ofresistivity, and the result is shown in Table.4. Winding was formed onthe composite soft magnetic material constituted of the ring-shapedheat-treated article, and magnetic flux density, coercive force, coreloss under conditions of magnetic flux density of 0.1 T and frequency of10 kHz, and core loss under conditions of magnetic flux density of 1.0 Tand frequency of 400 Hz were measured. The results are shown in Table 4.

Example 10

Polyimide resin in an amount of 1 mass % was added to, and mixed withthe oxide deposition film-coated iron silicide powder of the presentinvention produced in Example 8. The obtained mixed powder was chargedin moulds, and was press-molded into compacts, thereby a plate-shapedcompact having a dimension of length: 55 mm, width: 10 mm, andthickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were thermally hardened underconditions of a nitrogen atmosphere, temperature: 550° C., and retentiontime: 30 minutes. Thus, composite soft magnetic materials constituted ofa plate-shaped or ring-shaped heat-treated compact were produced. Thecomposite soft magnetic material constituted of the plate-shapedheat-treated article was subjected to measurement of resistivity, andthe result is shown in Table.4. The composite soft magnetic material wasobserved using a transmission electron microscope. As a result, ironparticle phase and grain boundary phase surrounding the iron particlephase were observed. From the electron beam diffraction pattern obtainedfrom the grain boundary phase, it was confirmed that the grain boundaryphase included crystalline MgO-dissolving wustite type phase.

Further, winding was formed on the composite soft magnetic materialconstituted of the ring-shaped heat-treated compact, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 1.5 T and frequency of 50 Hz, and core loss under conditionsof magnetic flux density of 1.0 T and frequency of 400 Hz were measured.The results are shown in Table 4.

Conventional Example 6

Polyimide resin in an amount of 1 mass % was added to, and mixed withthe conventional conversion treatment film-coated iron silicide powderproduced in Conventional Example 4 by chemically forming Mg-containingconversion treatment film on the surface of the iron silicide powder.The obtained mixed powder was charged in moulds, and was press-moldedinto compacts, thereby a plate-shaped compact having a dimension oflength: 55 mm, width: 10 mm, and thickness: 5 mm, and a ring-shapedcompact having a dimension of external diameter: 35 mm, internaldiameter: 25 mm, and height: 5 mm were formed. The obtained compactswere thermally hardened under conditions of a nitrogen atmosphere,temperature: 550° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated compact were produced. The composite soft magnetic materialconstituted of the plate-shaped heat-treated compact was subjected tomeasurement of resistivity, and the result is shown in Table.4. Windingwas formed on the composite soft magnetic material constituted of thering-shaped heat-treated compact, and magnetic flux density, coerciveforce, core loss under conditions of magnetic flux density of 0.1 T andfrequency of 10 kHz, and core loss under conditions of magnetic fluxdensity of 1.0 T and frequency of 400 Hz were measured. The results areshown in Table 4.

Example 11

PPS resin in an amount of 1 mass % was added to, and mixed with theoxide deposition film-coated iron silicide powder of the presentinvention produced in Example 8. The obtained mixed powder was chargedin moulds, and was press-molded into compacts, thereby a plate-shapedcompact having a dimension of length: 55 mm, width: 10 mm, andthickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were heat-treated under conditions ofa nitrogen atmosphere, temperature: 500° C., and retention time: 30minutes. Thus, composite soft magnetic materials constituted of aplate-shaped or ring-shaped heat-treated compact were produced. Thecomposite soft magnetic material constituted of the plate-shapedheat-treated article was subjected to measurement of resistivity, andthe result is shown in Table.4. The composite soft magnetic material wasobserved using a transmission electron microscope. As a result, ironparticle phase and grain boundary phase surrounding the iron particlephase were observed. From the electron beam diffraction pattern obtainedfrom the grain boundary phase, it was confirmed that the grain boundaryphase included crystalline MgO-dissolving wustite type phase.

Further, winding was formed on the composite soft magnetic materialconstituted of the ring-shaped heat-treated compact, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 0.1 T and frequency of 10 kHz, and core loss under conditionsof magnetic flux density of 1.0 T and frequency of 400 Hz were measured.The results are shown in Table 4.

Conventional Example 7

PPS resin in an amount of 1 mass % was added to, and mixed with theconventional conversion treatment film-coated iron silicide powderproduced in Conventional Example 4 by chemically forming Mg-containingconversion treatment film on the surface of the iron silicide powder.The obtained mixed powder was charged in moulds, and was press-moldedinto compacts, thereby a plate-shaped compact having a dimension oflength: 55 mm, width: 10 mm, and thickness: 5 mm, and a ring-shapedcompact having a dimension of external diameter: 35 mm, internaldiameter: 25 mm, and height: 5 mm were formed. The obtained compactswere heat-treated under conditions of a nitrogen atmosphere,temperature: 500° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated compact were produced. The composite soft magnetic materialconstituted of the plate-shaped heat-treated compact was subjected tomeasurement of resistivity, and the result is shown in Table.4. Windingwas formed on the composite soft magnetic material constituted of thering-shaped heat-treated compact, and magnetic flux density, coerciveforce, core loss under conditions of magnetic flux density of 0.1 T andfrequency of 10 kHz, and core loss under conditions of magnetic fluxdensity of 1.0 T and frequency of 400 Hz were measured. The results areshown in Table 4.

TABLE 4 PROPERTIES OF COMPOSITE SOFT MAGNETIC MATERIAL SPECIES ANDAMOUNT Flux OF ADDITION OF RESIN density Coersive Core Core SiliconePolyimide Density B_(10KA/m) force loss* loss** Resistivity TYPE resinresin PPS resin (g/cm³) (T) (A/m) (W/kg) (W/kg) (μΩm) EXAMPLE 8 — — —7.5 1.52 100 25 23 1000 CONVENTIONAL 4 — — — 7.4 1.50 150 — 60 30EXAMPLE 9 1 mass % — — 7.5 1.55 85 16 20 23000 CONVENTIONAL 5 — — 7.41.52 100 19 22 8000 EXAMPLE 10 — 1 mass % — 7.4 1.45 120 18 22 20000CONVENTIONAL 6 — — 7.4 1.47 170 22 25 5000 EXAMPLE 11 — — 1 mass % 7.41.44 130 19 23 21000 CONVENTIONAL 7 — — 7.3 1.41 180 23 26 6000 Coreloss* denotes core loss at flux density of 0.1 T and frequency of 10 kHzCore loss** denotes core loss at flux density of 1.0 T and frequency of400 Hz

From the result shown in Table 4, the following are understood. Wherecomposite soft magnetic materials produced using the oxide depositionfilm-coated iron silicide powder of the present invention produced inExample 8 is compared with the conventional composite soft magneticmaterial produced using conventional conversion treatment film-coatediron silicide powder produced in Comparative Example 4, no remarkabledifference can be observed in the density. On the other hand, comparedto the conventional composite soft magnetic material produced usingconventional conversion treatment film-coated iron silicide powderproduced in Conventional Example 4, composite soft magnetic materialsproduced using the oxide deposition film-coated iron silicide powder ofthe present invention produced in Example 8 have high magnetic fluxdensity, low coercive force, remarkably high resistivity, and thereforehas remarkably low core loss which is especially low as the frequencyincrease.

Where the composite soft magnetic materials produced in Example 9constituted of heat-treated compacts comprising oxide-deposition filmcoated iron silicide powder of the present invention and intergranularinsulation material composed of silicone resin is compared with thecomposite soft magnetic materials produced in Conventional Example 5constituted of heat-treated compacts comprising conventional conversiontreatment film-coated iron silicide powder and intergranular insulationmaterial composed of silicone resin, no remarkable difference can beobserved in the density. On the other hand, compared to the compositesoft magnetic materials produced in Conventional Example 5 constitutedof heat-treated compacts comprising conventional conversion treatmentfilm-coated iron silicide powder and intergranular insulation materialcomposed of silicone resin, composite soft magnetic materials producedin Example 9 constituted of heat-treated compacts comprisingoxide-deposition film coated iron silicide powder of the presentinvention and intergranular insulation material composed of siliconeresin have high magnetic flux density, low coercive force, remarkablyhigh resistivity, and therefore has remarkably low core loss which isespecially low as the frequency increase.

In addition, it is understood that similar results are obtained wherethe composite soft magnetic materials produced in Example 10 constitutedof heat-treated compacts comprising oxide-deposition film coated ironsilicide powder of the present invention and intergranular insulationmaterial composed of polyimide resin are compared with the compositesoft magnetic materials produced in Conventional Example 6 constitutedof heat-treated compacts comprising conventional conversion treatmentfilm-coated iron silicide powder and intergranular insulation materialcomposed of polyimide resin, and where the composite soft magneticmaterials produced in Example 11 constituted of heat-treated compactscomprising oxide-deposition film coated iron silicide powder of thepresent invention and intergranular insulation material composed of PPSresin are compared with the composite soft magnetic materials producedin Conventional Example 7 constituted of heat-treated compactscomprising conventional conversion treatment film-coated iron silicidepowder and intergranular insulation material composed of PPS resin.

Example 12

The oxide deposition film-coated iron silicide powder of the presentinvention produced in Example 8 was pretreated with silane couplingagent. After that, silicone resin diluted in organic solvent was addedto the pretreated powder such that 1 mass % of silicone resin was added.By drying the powder at 200° C., mixed powder was prepared. 0.1 mass %of zinc stearate was added to, and mixed with the mixed powder, and themixed powder was molded into compacts, thereby a ring-shaped compacthaving a dimension of external diameter: 35 mm, internal diameter: 25mm, and height: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 50 mm, internal diameter: 25 mm, and height: 25 mmwere formed. The obtained compacts were subjected to strain-relief heattreatment at 850° C. in a vacuum atmosphere. Thus, composite softmagnetic materials constituted of a ring-shaped heat-treated compacthaving a small external diameter and a ring-shaped compact having alarge external diameter were produced. Under the observation of thesecomposite soft magnetic materials using a transmission electronmicroscope, iron particle phase and grain boundary phase surrounding theiron particle phase were observed. From the electron beam diffractionpattern obtained from the grain boundary phase, it was confirmed thatthe grain boundary phase included crystalline MgO-dissolving wustitetype phase.

Winding was formed on the ring-shaped heat-treated compact having thesmall diameter, and DC magnetic property and core loss under conditionsof 0.1 T and 10 kHz were measured. The results are shown in Table 5.Using the ring-shaped heat-treated compact having the small externaldiameter, inductance at 20 kHz was measured while superimposing directcurrent of 20 A, and AC magnetic permeability was determined. The resultis shown in Table 5.

Next, winding was formed using the ring-shaped heat-treated compacthaving the large external diameter, and a reactor having almost constantinductance was produced. The reactor was connected to a switching powersupply equipped with a general type of active filter. Efficiencies (%)of output power versus input power of 1000 W and 1500 W were measured.The results are shown in Table 5.

Example 13

As a stock powder, gas-water-atomized iron silicide powder having acomposition containing Si:6.5 mass % and the balance consisting of Feand unavoidable impurities, having a mean grain size of 55 μm, andhaving nearly spherical particle shape was prepared. In addition, Mgpowder having a mean grain size of 40 μm was prepared. Surface oxidationtreatment of the gas-water-atomized powder was performed underconditions of retaining 1 hour at 220° C. in air. A mixed powder wasproduced by adding the Mg powder to the oxidation-treatedgas-water-atomized iron silicide powder in such a proportion that thegas-water-atomized iron silicide powder: Mg powder=99.6:0.4, and mixingthe powder. The mixed powder was retained at a temperature of 650° C.under a pressure of 1×10⁻⁵ MPa for 1.5 hour. Thus, depositionoxide-film-coated iron silicide powder of the present inventioncomprising gas-water-atomized iron silicide powder and oxide depositionfilm coated on the surface of the iron silicide powder was produced.

Concentration distributions of Mg, Si, O, and Fe in depth direction ofthe deposition film of the deposition film-coated iron silicide powderwere examined using an Auger electron spectroscopic analyzer. As aresult, it was confirmed that the deposition film had concentrationgradients where Mg and O decreases from the surface towards the interiordirection, Fe increased towards the interior direction, and the film hada concentration gradient of Si where Si content increased in thevicinity of the outermost surface such that a portion close to theoutermost surface showed as a high Si content.

In addition, the oxide deposition film formed on the surface of thedeposition-film coated iron silicide powder was analyzed using a X-rayphotoelectron spectroscopic analyzer, and bonding energies wereexamined. As a result, it was confirmed that metallic Fe or Fe—Si alloywere included in the deposition film.

Therefore, the followings can be understood. The oxide deposition filmformed on the surface of the oxide deposition-film coated iron silicidepowder of the present invention is a Mg—Si—Fe—O quaternary-based oxidedeposition film comprising Mg, Si, Fe, and O. The Mg—Si—Fe—Oquaternary-based oxide deposition film of the present invention hasconcentration gradients where Mg and O decreases from the surfacetowards the interior direction, Fe increases towards the interiordirection, and has a concentration gradient of Si where Si contentincreases in the vicinity of the outermost surface such that a portionclose to the outermost surface shows as a high Si content. Metallic Feor Fe—Si alloy is contained. In addition, the texture of the depositionfilm in the deposition film-coated iron silicide powder was observedusing a transmission electron microscope, and thickness and maximumgrain size of the oxide deposition film were measured. As a result, theoxide deposition film had an average thickness of 60 nm and maximumgrain size of 20 nm.

The oxide deposition film-coated iron silicide powder of the presentinvention was pretreated with silane coupling agent. After that,silicone resin diluted in organic solvent was added to the pretreatedpowder such that 1 mass % of silicone resin was added. By drying thepowder at 250° C., mixed powder was prepared. 0.1 mass % of zincstearate was added to, and mixed with the mixed powder, and the mixedpowder was molded into compacts, thereby a ring-shaped compact having adimension of external diameter: 35 mm, internal diameter: 25 mm, andheight: 5 mm, and a ring-shaped compact having a dimension of externaldiameter: 50 mm, internal diameter: 25 mm, and height: 25 mm wereformed. These compacts were subjected to strain-relief heat treatment at850° C. in a vacuum atmosphere. Thus, composite soft magnetic materialsconstituted of a ring-shaped heat-treated compact having a smallexternal diameter and a ring-shaped compact having a large externaldiameter were produced. Under the observation of these composite softmagnetic materials using a transmission electron microscope, ironparticle phase and grain boundary phase surrounding the iron particlephase were observed. From the electron beam diffraction pattern obtainedfrom the grain boundary phase, it was confirmed that the grain boundaryphase included crystalline MgO-dissolving wustite type phase.

Winding was formed on the ring-shaped heat-treated compact having thesmall diameter, and DC magnetic property and core loss under conditionsof 0.1 T and 10 kHz were measured. The results are shown in Table 5.Using the ring-shaped heat-treated compact having the small externaldiameter, inductance at 20 kHz was measured while superimposing directcurrent of 20 A, and AC magnetic permeability was determined. The resultis shown in Table 5.

Next, winding was formed using the ring-shaped heat-treated compacthaving the large external diameter, and a reactor having almost constantinductance was produced. The reactor was connected to a switching powersupply equipped with a general type of active filter. Efficiencies (%)of output powers versus input powers of 1000 W and 1500 W were measured.The results are shown in Table 5.

Gas-water-atomized iron silicide powder prepared in Example, having acomposition containing Si:3 mass % and the balance consisting of Fe andunavoidable impurities, and having a mean grain size of 70 μm waspretreated with silane coupling agent. After that, mixed powder wasproduced such that the iron silicide powder was mixed with 1.0 mass % ofsilicone resin and 0.2 mass % of MgO powder. The obtained mixed powderwas compacted, and the compacts were subjected to strain-relief heattreatment at 850° C. in a vacuum atmosphere, thereby heat-treatedcompacts having the same shapes and dimensions as Example 12 wereproduced.

Winding was formed on the ring-shaped heat-treated compact having thesmall diameter, and DC magnetic property and core loss under conditionsof 0.1 T and 10 kHz were measured. The results are shown in Table 5.Using the ring-shaped heat-treated compact having the small externaldiameter, inductance at 20 kHz was measured while superimposing directcurrent of 20 A, and AC magnetic permeability was determined. The resultis shown in Table 5.

Next, winding was formed using the ring-shaped heat-treated compacthaving the large external diameter, and a reactor having almost constantinductance was produced. The reactor was connected to a switching powersupply equipped with a general type of active filter. Efficiencies (%)of output power versus input power of 1000 W and 1500 W were measured.The results are shown in Table 5.

TABLE 5 Switching power Flux supply density Coercive Core INPUT B_(10K)force loss* Permeability POWER Efficiency Type (T) Hc(A/m) (W/kg) 20 A,20 kHz (W) (%) EXAMPLE 12 1.55 83 16 31 1000 92.8 1500 92.1 EXAMPLE 131.56 80 16 32 1000 93.1 1500 92.5 CONVENTIONAL 1.53 103 19 27 1000 91.6EXAMPLE 8 1500 91.0

From the results shown in Table 5, the following are understood.Compared to the composite soft magnetic materials of ConventionalExample produced using iron silicide powder, composite soft magneticmaterials of Examples 12 to 13 produced using the oxide depositionfilm-coated iron silicide powder of the present invention have lowcoercive force, low core loss, and excellent DC superimposing property.In addition, compared to the switching power supply connected to thereactor using composite soft magnetic material produced in ConventionalExample 8, efficiency is increased in switching power supplies connectedto the reactors using composite soft magnetic materials produced inExamples 12 to 13. Therefore, properties are further increased inreactors having a core constituted of composite soft magnetic materialmade of heat-treated compact comprising the oxide deposition film-coatediron silicide powder of the present invention and intergranular siliconeresin.

Example 8

As a stock powders, iron based Fe—Si-based soft magnetic powder having acomposition containing Si:1 mass % and the balance consisting of Fe andunavoidable impurities, and having a mean grain size of 75 μm, and puresilicon powder having a mean grain size of 1 μm or less were prepared.In addition, Mg powder having a mean grain size of 50 μm was prepared.

Firstly, a mixed powder was produced by blending and mixing the puresilicon powder with the iron-based Fe—Si-based soft magnetic powder insuch a proportion that the iron-based Fe—Si-based soft magnetic powder:pure Si powder=99.5 mass %: 0.5 mass %. By heat treating the obtainedmixed powder using conditions of hydrogen atmosphere, temperature: 950°C., and retention time: 1 hour, high concentration Si diffused-layer wasformed on the surface of iron-based Fe—Si-based soft magnetic powder.After that, by retaining the powder at 250° C. in air, surface oxidizediron-based Fe—Si-based soft magnetic powder having an oxide layer on thesurface of the high concentration Si diffused-layer was produced.

A mixed powder was produced by blending and mixing the prepared Mgpowder with the surface oxidized iron-based Fe—Si-based soft magneticpowder in such a proportion that the surface oxidized iron-basedFe—Si-based soft magnetic powder: Mg powder=99.8 mass %: 0.2 mass %. Byretaining the obtained mixed powder for 1 hour at a temperature of 650°C. under a pressure of 2.7×10⁻⁴ MPa while tumbling the mixed powder,oxide deposition film-coated iron-based Fe—Si-based soft magnetic powderof the present invention (hereafter referred to as oxide depositionfilm-coated powder of the invention) 1 having an oxide deposition filmcomprising Mg, Si, Fe and O formed in the surface of the iron-basedFe—Si-based soft magnetic powder was produced.

By the analysis using an X-ray photoelectron spectroscopic analyzer andexamination of bonding energies, it was confirmed that the oxidedeposition film formed in the oxide deposition film-coated powder 1 ofthe present invention was an oxide deposition film comprising Mg, Fe,Si, and O, and metallic Fe and Fe—Si alloy were included in the matrixof the oxide deposition film. Texture of the oxide deposition film inthe oxide deposition film-coated powder of the present invention wasobserved using a transmission electron microscope and a thickness andmaximum grain size of the oxide deposition film were determined. Theresults are shown in Table 6. In addition, from the electron beamdiffraction patterns, it was confirmed that Mg and O were contained ascrystalline MgO dissolving wustite type phase in the oxide depositionfilm comprising Mg, Fe, Si, and O.

Concentration distributions of Mg, O, Si, and Fe in depth direction ofthe oxide deposition film comprising Mg, Si, Fe, and O were analyzedusing an Auger electron spectroscopic analyzer. The results are shown inTable 6. FIG. 8 shows a analytical graph obtained by analyzing thedistributions of Mg, O, Si, and Fe in depth direction of the oxidedeposition film comprising Mg, Si, Fe, and O of the oxide depositionfilm-coated powder 1 of the invention. In the horizontal axis of FIG. 8,Etching time 0 corresponds to the outermost surface. In FIG. 8, it isunderstood that the oxide deposition film comprising Mg, Si, Fe, and Oshows concentration gradients where Mg and O increases towards thesurface, Fe content decreases towards the surface, and Si increases inthe vicinity of the outermost surface such that a portion close to theoutermost surface shows as a high Si content.

The obtained oxide deposition film-coated powder 1 of the presentinvention was charged in moulds, and was press-molded into compacts,thereby a plate-shaped compact having a dimension of length: 55 mm,width: 10 mm, and thickness: 5 mm, and a ring-shaped compact having adimension of external diameter: 35 mm, internal diameter: 25 mm, andheight: 5 mm were formed. The obtained compacts were heat-treated underconditions of a nitrogen atmosphere, temperature: 500° C., and retentiontime: 30 minutes. Thus, composite soft magnetic materials constituted ofa plate-shaped or ring-shaped heat-treated article were produced. Thecomposite soft magnetic material constituted of the plate-shapedheat-treated article was subjected to measurement of resistivity, andthe result is shown in Table.6. Winding was formed on the composite softmagnetic material constituted of the ring-shaped heat-treated article,and magnetic flux density, coercive force, core loss under conditions ofmagnetic flux density of 1.5 T and frequency of 50 Hz, and core lossunder conditions of magnetic flux density of 1.0 T and frequency of 400Hz were measured. The results are shown in Table 6.

By chemically forming an Mg-containing ferrite oxide layer on thesurface of the iron-based Fe—Si-based soft magnetic powder prepared inExample 14, conventional Mf-containing ferrite oxide-coated iron-basedFe—Si-based soft magnetic powder (hereafter referred to as conventionaloxide deposition film-coated powder) was produced. The obtainedconventional ferrite oxide deposition film-coated powder was charged inmoulds, and was press-molded into compacts, thereby a plate-shapedcompact having a dimension of length: 55 mm, width: 10 mm, andthickness: 5 mm, and a ring-shaped compact having a dimension ofexternal diameter: 35 mm, internal diameter: 25 mm, and height: 5 mmwere formed. The obtained compacts were heat-treated under conditions ofa nitrogen atmosphere, temperature: 500° C., and retention time: 30minutes. Thus, composite soft magnetic materials constituted of aplate-shaped or ring-shaped heat-treated article were produced. Thecomposite soft magnetic material constituted of the plate-shapedheat-treated article was subjected to measurement of resistivity, andthe result is shown in Table.6. Winding was formed on the composite softmagnetic material constituted of the ring-shaped heat-treated article,and magnetic flux density, coercive force, core loss under conditions ofmagnetic flux density of 1.5 T and frequency of 50 Hz, and core lossunder conditions of magnetic flux density of 1.0 T and frequency of 400Hz were measured. The results are shown in Table 6.

TABLE 6 CONVENTIONAL TYPE EXAMPLE 14 EXAMPLE 9 Properties of Thickness(nm) 100 — Mg—Si—Fe—O Maximum 30 — quaternary-based grain size oxidedeposition film Properties of Density 7.6 7.4 composite (g/cm3) softmagnetic Flux density 1.57 1.50 material B10KA/m (T) Coercive force 90145 (A/m) Core loss* 23 — (W/kg) Core loss** 20 58 (W/kg) Resistivity1200 35 (μΩm) Core loss* denotes core loss at flux density of 1.5 T andfrequency of 50 Hz Core loss** denotes core loss at flux density of 1.0T and frequency of 400 Hz

From the results shown in Table 6, the following are understood. Wherecomposite soft magnetic materials produced using oxide depositionfilm-coated powder 1 of the present invention produced in Example 14 arecompared with the conventional composite soft magnetic materialsproduced using Mg-containing ferrite oxide-coated iron-based Fe—Si-basedsoft magnetic powder produced in Conventional Example 9, no remarkabledifference can be observed in the density. On the other hand, comparedto the conventional composite soft magnetic material produced usingMg-containing ferrite oxide-coated iron-based Fe—Si-based soft magneticpowder produced in Conventional Example 9, composite soft magneticmaterial produced using oxide deposition film-coated powder 1 of thepresent invention produced in Example 14 has high magnetic flux density,low coercive force, remarkably high resistivity, and therefore hasremarkably low core loss which is especially low as the frequencyincrease.

Example 15

As stock powders, iron-based Fe—Si-based soft magnetic powders eachhaving a grain size shown in Table 7 and having a composition containingSi:1 mass % and the balance consisting of Fe and unavoidable impuritieswere prepared. In addition, pure silicon powder having a mean grain sizeof 1 μm or less and Mg powder having a mean grain size of 50 μm wereprepared.

Mixed powders were produced by blending and mixing the pure siliconpowder with the each of the iron-based Fe—Si-based soft magnetic powdershaving different grain size in such a proportion that the iron-basedFe—Si-based soft magnetic powder: pure Si powder=97 mass %: 2 mass %. Byheat treating the obtained mixed powders using conditions of hydrogenatmosphere, temperature: 950° C., and retention time: 1 hour, a highconcentration Si diffused-layer was formed on the surface of iron-basedFe—Si-based soft magnetic powders. After that, by retaining the powderat 220° C. in air, surface-oxidized iron-based Fe—Si-based soft magneticpowders having an oxide layer on the surface of the high concentrationSi diffused-layer were produced.

Mixed powders were produced by blending and mixing the prepared Mgpowder with the surface-oxidized iron-based Fe—Si-based soft magneticpowders in such a proportion that the surface-oxidized iron-basedFe—Si-based soft magnetic powder: Mg powder=99.8 mass %: 0.2 mass %. Byperforming a treatment retaining the obtained mixed powder for 1 hour ata temperature of 650° C. under a pressure of 2.7×10⁻⁴ MPa while tumblingthe mixed powder (hereafter, the treatment comprising production of amixed powder in such a proportion that the surface-oxidized iron-basedFe—Si-based soft magnetic powder: Mg powder=99.8 mass %: 0.2 mass %, andretaining the obtained mixed powder for 1 hour at a temperature of 650°C. under a pressure of 2.7×10⁻⁴ MPa while tumbling the mixed powder isreferred to as Mg-coating treatment), methods 1 to 3 of the presentinvention for producing oxide deposition film-coated iron-basedFe—Si-based soft magnetic powders of the present invention having anoxide deposition film comprising Mg, Si, Fe and O formed in the surfaceof the iron-based Fe—Si-based soft magnetic powder were performed.

By the analysis using an X-ray photoelectron spectroscopic analyzer andexamination of bonding energies, it was confirmed that the oxidedeposition films formed on the oxide deposition film-coated powdersobtained by methods 1 to 3 of the present invention were oxidedeposition films comprising Mg, Fe, Si, and O, and metallic Fe and Fe—Sialloy were included in the matrices of the oxide deposition films. Thetextures of the oxide deposition films in the oxide depositionfilm-coated iron-based Fe—Si-based soft magnetic powders were observedusing a transmission electron microscope. From the electron beamdiffraction patterns, it was confirmed that Mg and were contained ascrystalline MgO-dissolving wustite type phases in the oxide depositionfilms comprising Mg, Fe, Si, and O. Concentration distributions of Mg,O, Si, and Fe in depth direction of the oxide deposition filmscomprising Mg, Si, Fe, and O were analyzed using an Auger electronspectroscopic analyzer, and it was confirmed that the oxide depositionfilms comprising Mg, Si, Fe, and O showed concentration gradients whereMg and O increases towards the surface, Fe content decreases towards thesurface, and Si increases in the vicinity of the outermost surface suchthat a portion close to the outermost surface shows as a high Sicontent.

By adding silicone resin in a blending ratio of 2 mass % to oxidedeposition film-coated iron-based Fe—Si-based soft magnetic powdersobtained by the methods 1 to 3 of the present invention, and mixing thepowders, resin-coated composite powders each having a coating ofsilicone resin on the surface of the oxide deposition film-coatediron-based Fe—Si-based soft magnetic powders were produced. Theresin-coated composite powders were charged in moulds heated at 120° C.,and were press-molded into compacts, thereby plate-shaped compactshaving a dimension of length: 55 mm, width: 10 mm, and thickness: 5 mm,and ring-shaped compacts having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of vacuum atmosphere,temperature: 700° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magneticmaterials constituted of the plate-shaped heat-treated articles weresubjected to measurement of resistivity, and the results are shown inTable.6. Windings were formed on the composite soft magnetic materialsconstituted of the ring-shaped heat-treated articles, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 0.1 T and frequency of 20 Hz were measured. The results areshown in Table 7.

Conventional Example 10

As stock powders, iron-based Fe—Si-based soft magnetic powders eachhaving a grain size shown in Table 7 and having a composition containingSi:1 mass % and the balance consisting of Fe and unavoidable impuritieswere prepared. Without performing the Mg coating treatment, siliconeresin in a blending ratio of 2 mass % was added to, and mixed with theiron-based Fe—Si-based soft magnetic powders. Thus, resin-coatedcomposite powders each having a coating of silicone resin on the surfaceof the iron-based Fe—Si-based soft magnetic powders were produced. Theresin-coated composite powders were charged in moulds heated at 120° C.,and were press-molded into compacts, thereby plate-shaped compactshaving a dimension of length: 55 mm, width: 10 mm, and thickness: 5 mm,and ring-shaped compacts having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of vacuum atmosphere,temperature: 700° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magneticmaterials constituted of the plate-shaped heat-treated articles weresubjected to measurement of resistivity, and the results are shown inTable.7. Windings were formed on the composite soft magnetic materialsconstituted of the ring-shaped heat-treated articles, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 0.1 T and frequency of 20 Hz were measured. The results areshown in Table 7.

TABLE 7 Mean Magnetic properties grain size of Flux Fe—1% Si densityCoercive Core stock powder Mg coating B_(10KA/m) force loss* ResistivityType (μm) treatment (T) (A/m) (W/kg) (μΩm) Method 1 60 performed 1.30 9546 25000 of the 2 150 performed 1.32 90 41 24000 invention 3 300performed 1.35 80 39 20000 Conventional 150 not 1.32 130 1000 150 method1 performed Core loss* denotes core loss at flux density of 0.1 T andfrequency of 20 kHz

It can be understood that compared to the composite soft magneticmaterial produced in conventional method 1, composite soft magneticmaterials produced in accordance with the methods 1 to 3 of the presentinvention have high magnetic flux density, low coercive force,remarkably high resistivity, and therefore have remarkably low core losswhich is especially low as the frequency increases.

Example 16

As stock powders, iron-based Fe—Si-based soft magnetic powders eachhaving a grain size shown in Table 8 and having a composition containingSi:3 mass % and the balance consisting of Fe and unavoidable impuritieswere prepared. In addition, pure silicon powder having a mean grain sizeof 1 μm or less and Mg powder having a mean grain size of 50 μm wereprepared.

Mixed powders were produced by blending and mixing the pure siliconpowder with the each of the iron-based Fe—Si-based soft magnetic powdershaving different grain size in such a proportion that the iron-basedFe—Si-based soft magnetic powder: pure Si powder=99.5 mass %: 0.5 mass%. By heat treating the obtained mixed powders using conditions ofhydrogen atmosphere, temperature: 950° C., and retention time: 1 hour,high concentration Si diffused-layer was formed on the surface ofiron-based Fe—Si-based soft magnetic powders. After that, by retainingthe powder at 220° C. in air, surface-oxidized iron-based Fe—Si-basedsoft magnetic powders having an oxide layer on the surface of the highconcentration Si diffused-layer were produced.

By performing the Mg coating treatment of the surface-oxidizediron-based Fe—Si-based soft magnetic powders methods 4 to 6 of thepresent invention for producing oxide deposition film-coated iron-basedFe—Si-based soft magnetic powders of the present invention having anoxide deposition film comprising Mg, Si, Fe and O formed in the surfaceof the iron-based Fe—Si-based soft magnetic powder were performed.

By the analysis using an X-ray photoelectron spectroscopic analyzer andexamination of bonding energies, it was confirmed that the oxidedeposition films formed in the oxide deposition film-coated powdersobtained by methods 4 to 6 of the present invention were oxidedeposition films comprising Mg, Fe, Si, and O, and metallic Fe and Fe—Sialloy were included in the matrices of the oxide deposition films.Textures of the oxide deposition films in the oxide depositionfilm-coated iron-based Fe—Si-based soft magnetic powders were observedusing a transmission electron microscope. From the electron beamdiffraction patterns, it was confirmed that Mg and O were contained ascrystalline MgO dissolving wustite type phases in the oxide depositionfilms comprising Mg, Fe, Si, and O. Concentration distributions of Mg,O, Si, and Fe in depth direction of the oxide deposition filmscomprising Mg, Si, Fe, and O were analyzed using an Auger electronspectroscopic analyzer, and it was confirmed that the oxide depositionfilms comprising Mg, Si, Fe, and O showed concentration gradients whereMg and O increases towards the surface, Fe content decreases towards thesurface, and Si increases in the vicinity of the outermost surface suchthat a portion close to the outermost surface shows as a high Sicontent.

By adding silicone resin in a blending ratio of 2 mass % to oxidedeposition film-coated iron-based Fe—Si-based soft magnetic powdersobtained by the methods 4 to 6 of the present invention, and mixing thepowders, resin-coated composite powders each having a coating ofsilicone resin on the surface of the oxide deposition film-coatediron-based Fe—Si-based soft magnetic powders were produced. Theresin-coated composite powders were charged in moulds heated at 120° C.,and were press-molded into compacts, thereby plate-shaped compactshaving a dimension of length: 55 mm, width: 10 mm, and thickness: 5 mm,and ring-shaped compacts having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of vacuum atmosphere,temperature: 700° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magneticmaterials constituted of the plate-shaped heat-treated articles weresubjected to measurement of resistivity, and the results are shown inTable.8. Windings were formed on the composite soft magnetic materialsconstituted of the ring-shaped heat-treated articles, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 0.1 T and frequency of 20 Hz were measured. The results areshown in Table 8.

Conventional Example 11

As stock powders, iron-based Fe—Si-based soft magnetic powders eachhaving a grain size shown in Table 8 and having a composition containingSi:1 mass % and the balance consisting of Fe and unavoidable impuritieswere prepared. Without performing the Mg coating treatment, siliconeresin in a blending ratio of 3 mass % was added to, and mixed with theiron-based Fe—Si-based soft magnetic powders. Thus, resin-coatedcomposite powders each having a coating of silicone resin on the surfaceof the iron-based Fe—Si-based soft magnetic powders were produced. Theresin-coated composite powders were charged in moulds heated at 120° C.,and were press-molded into compacts, thereby plate-shaped compactshaving a dimension of length: 55 mm, width: 10 mm, and thickness: 5 mm,and ring-shaped compacts having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of vacuum atmosphere,temperature: 700° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magneticmaterials constituted of the plate-shaped heat-treated articles weresubjected to measurement of resistivity, and the results are shown inTable.8. Windings were formed on the composite soft magnetic materialsconstituted of the ring-shaped heat-treated articles, and magnetic fluxdensity, coercive force, core loss under conditions of magnetic fluxdensity of 0.1 T and frequency of 20 Hz were measured. The results areshown in Table 8.

TABLE 8 Mean grain size Magnetic properties of Fe—1% Si Flux CoerciveCore stock powder Mg coating density force loss* Resistivity Type (μm)treatment B_(10KA/m) (T) (A/m) (W/kg) (μΩm) Method 4 60 performed 1.43100 55 21000 of the 5 150 performed 1.43 97 52 20000 invention 6 300performed 1.47 83 47 17000 Conventional 150 not 1.43 140 9900 115 method2 performed Core loss* denotes core loss at flux density of 0.1 T andfrequency of 20 kHz

It can be understood that compared to the composite soft magneticmaterial produced in conventional method 2, composite soft magneticmaterials produced in accordance with the methods 4 to 6 of the presentinvention have high magnetic flux density, low coercive force,remarkably high resistivity, and therefore have remarkably low core losswhich is especially low as the frequency increases.

Example 17

As stock powders, Fe powders each having grain size shown in Table 9were prepared. In addition, pure Si powder having a mean grain size of 1μm or less and Mg powder having a grain size of 50 μm were prepared.

Mixed powders were produced by blending and mixing the pure siliconpowder with the each of the Fe powders having different grain size insuch a proportion that the Fe powder: pure Si powder=97 mass %: 3 mass%. By heat treating the obtained mixed powders using conditions ofhydrogen atmosphere, temperature: 950° C., and retention time: 1 hour,high concentration Si diffused-layer was formed on the surface ofiron-based Fe—Si-based soft magnetic powders. After that, by retainingthe powders at 220° C. in air, surface-oxidized iron-based Fe—Si-basedsoft magnetic powders having an oxide layer on the surface of the highconcentration Si diffused-layer were produced.

By performing the Mg coating treatment of the surface-oxidizediron-based Fe—Si-based soft magnetic powders, methods 7 to 9 of thepresent invention for producing oxide deposition film-coated iron-basedFe—Si-based soft magnetic powders of the present invention having anoxide deposition film comprising Mg, Si, Fe and O formed in the surfaceof the iron-based Fe—Si-based soft magnetic powder were performed.

By the analysis using an X-ray photoelectron spectroscopic analyzer andexamination of bonding energies, it was confirmed that the oxidedeposition films formed on the oxide deposition film-coated powdersobtained by methods 7 to 9 of the present invention were oxidedeposition films comprising Mg, Fe, Si, and O, and metallic Fe and Fe—Sialloy were included in the matrices of the oxide deposition films.Textures of the oxide deposition films in the oxide depositionfilm-coated iron-based Fe—Si-based soft magnetic powders were observedusing a transmission electron microscope. From the electron beamdiffraction patterns, it was confirmed that Mg and O were contained ascrystalline MgO dissolving wustite type phases in the oxide depositionfilms comprising Mg, Fe, Si, and O. Concentration distributions of Mg,O, Si, and Fe in depth direction of the oxide deposition filmscomprising Mg, Si, Fe, and O were analyzed using an Auger electronspectroscopic analyzer, and it was confirmed that the oxide depositionfilms comprising Mg, Si, Fe, and O showed concentration gradients whereMg and O increases towards the surface, Fe content decreases towards thesurface, and Si increases in the vicinity of the outermost surface suchthat a portion close to the outermost surface shows as a high Sicontent.

By adding silicone resin in a blending ratio of 2 mass % to oxidedeposition film-coated iron-based Fe—Si-based soft magnetic powdersobtained by the methods 7 to 9 of the present invention, and mixing thepowders, resin-coated composite powders each having a coating ofsilicone resin on the surface of the oxide deposition film-coatediron-based Fe—Si-based soft magnetic powders were produced. Theresin-coated composite powders were charged in moulds heated at 120° C.,and were press-molded into compacts, thereby plate-shaped compactshaving a dimension of length: 55 mm, width: 10 mm, and thickness: 5 mm,ring-shaped compacts having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm, and ring-shaped compactshaving a dimension of external diameter: 50 mm, internal diameter: 25mm, and height: 25 mm were formed. The obtained compacts wereheat-treated under conditions of vacuum atmosphere, temperature: 700°C., and retention time: 30 minutes. Thus, composite soft magneticmaterials constituted of a plate-shaped or ring-shaped heat-treatedarticle were produced. The composite soft magnetic materials constitutedof the plate-shaped heat-treated articles were subjected to measurementof resistivity, and the results are shown in Table.9. Windings wereformed on the composite soft magnetic materials constituted of thering-shaped heat-treated articles having the small diameter, andmagnetic flux density, coercive force, core loss under conditions ofmagnetic flux density of 0.1 T and frequency of 20 Hz were measured. Theresults are shown in Table 9.

Using the ring-shaped heat-treated compact having the small externaldiameter, inductance at 20 kHz was measured while superimposing directcurrent of 20 A, and AC magnetic permeability was determined. Theresults are shown in Table 10. Next, winding was formed on thering-shaped heat-treated compact having the large external diameter, anda reactor having almost constant inductance was produced. The reactorwas connected to a switching power supply equipped with a general typeof active filter. Efficiencies (%) of output power versus input power of1000 W and 1500 W were measured. The results are shown in Table 10.

Conventional Example 12

As stock powder, Fe powders having a grain size shown in Table 8 wasprepared. Without performing the Mg coating treatment, silicone resin ina blending ratio of 2 mass % was added to, and mixed with the Fe powder.Thus, resin-coated Fe powder having a coating of silicone resin on thesurface of the Fe powder was produced. The resin-coated Fe powder wascharged in moulds heated at 120° C., and was press-molded into compacts,thereby a plate-shaped compact having a dimension of length: 55 mm,width: 10 mm, and thickness: 5 mm, ring-shaped compact having adimension of external diameter: 35 mm, internal diameter: 25 mm, andheight: 5 mm, and ring-shaped compact having a dimension of externaldiameter: 50 mm, internal diameter: 25 mm, and height: 25 mm wereformed. The obtained compacts were heat-treated under conditions ofvacuum atmosphere, temperature: 700° C., and retention time: 30 minutes.Thus, composite soft magnetic materials constituted of a plate-shaped orring-shaped heat-treated compact were produced. The composite softmagnetic material constituted of the plate-shaped heat-treated compactwas subjected to measurement of resistivity, and the results are shownin Table.9. Winding was formed on the composite soft magnetic materialconstituted of the ring-shaped heat-treated compact having the smalldiameter, and magnetic flux density, coercive force, core loss underconditions of magnetic flux density of 0.1 T and frequency of 20 Hz weremeasured. The results are shown in Table 9.

Using the ring-shaped heat-treated compact having the small externaldiameter, inductance at 20 kHz was measured while superimposing directcurrent of 20 A, and AC magnetic permeability was determined. Theresults are shown in Table 7. Next, winding was formed on thering-shaped heat-treated compact having the large external diameter, anda reactor having almost constant inductance was produced. The reactorwas connected to a switching power supply equipped with a general typeof active filter. Efficiencies (%) of output power versus input power of1000 W and 1500 W were measured. The results are shown in Table 10.

TABLE 9 Mean grain size Magnetic properties of Fe Flux Coercive Corestock powder Mg coating density force loss* Resistivity Type (μm)treatment B_(10KA/m) (T) (A/m) (W/kg) (μΩm) Method 7 80 performed 1.50115 62 18000 of the 8 150 performed 1.52 100 68 15000 invention 9 300performed 1.55 90 75 12000 Conventional 150 not 1.51 150 1000 80 method3 performed Core loss* denotes core loss at flux density of 0.1 T andfrequency of 20 kHz

TABLE 10 Switching power Flux Core supply density Coercive loss* INPUTB_(10K) force W1/10k Permeability POWER Efficiency Type (T) Hc (A/m)(W/kg) 20 A, 20 kHz (W) (%) EXAMPLE 17 1.55 90 17 32 1000 92.7 1500 91.9CONVENTIONAL 1.51 150 30 28 1000 89.0 EXAMPLE 12 1500 88.0

It can be understood that compared to the composite soft magneticmaterial produced in conventional method 3, composite soft magneticmaterials produced in accordance with the methods 7 to 9 of the presentinvention have high magnetic flux density, low coercive force,remarkably high resistivity, and therefore has remarkably low core losswhich is especially low as the frequency increases.

Example 18

As stock powder, pure iron powder having mean grain size of 70 μm andcontaining trace amount of sulfur as unavoidable impurity was prepared.In addition, Mg powder having a mean grain size of 50 μm was prepared.

Firstly, oxidation-treated iron powder was produced by performingoxidation treatment by retaining the pure iron powder at 220° C. for 2hours in air. A mixed powder was produced by adding the prepared Mgpowder to the oxidation-treated iron powder in a proportion ofoxidation-treated iron powder: Mg powder=99.8 mass %: 0.3 mass %, andmixing the powder. The obtained mixed powder was retained at atemperature of 650° C. under a pressure of 2.7×10⁻⁴ MPa for 1 hour, andfurther retained at a temperature of 200° C. for 1 hour in air. Thus,Mg-containing iron oxide film-coated iron powder having a coating ofdeposition film on the surface of iron powder was produced. By theanalysis of bonding energies by analyzing the deposition film formed onthe surface of Mg-containing oxide film-coated iron powder using anX-ray photoelectron spectroscopic analyzer, it was confirmed that thedeposition film was a Mg—Fe—O ternary-based oxide deposition film atleast containing (Mg, Fe)O.

Boundary portion between the iron powder and the Mg—Fe—O ternary-basedoxide deposition film of the Mg-containing iron-oxide coated iron powderwas examined by a method using an Auger electron spectroscopic analyzer.As a result, a sulfur peak of Auger electron spectrum obviously higherthan the background constituted of impurity (background) sulfurcontained in the central portion of iron powder was obviously detectedin the boundary portion between the deposition film and iron powder.Therefore, the presence of a sulfur-enriched layer containing a higherconcentration of sulfur than that of the core portion of iron powder wasconfirmed in the boundary portion between the deposition film and ironpowder. As a result of observation of texture of the Mg—Fe—Oternary-based oxide deposition film at least containing (Mg, Fe)O formedon the Mg-containing oxide film-coated iron powder using a transmissionelectron microscope, it was confirmed that the deposition film had anaverage thickness of 60 nm and maximum grain size of 40 nm.

Prehydrosys alkoxysilane solution added with water and hydrochloric acidand magnesium-alkoxide solution were prepared. By mixing the solutionsin such a volumetric ratio that prehydrosys alkoxysilane solution:1magnesium-alkoxide solution:2, mixed oxide sol-solution of MgO and SiO₂was produced. The mixed oxide sol-solution of MgO and SiO₂ was added to,and mixed with the preliminary produced Mg-containing iron oxide-filmcoated iron powder, such that, in reduced mass of a mixture of MgO andSiO₂, 0.2 mass % was added in the mixed powder. By drying the mixedpowder by heating at a temperature of 150° C., composite soft magneticpowder of the present invention having coating of MgO—SiO₂ compositeoxide film composed of 2MgO.SiO₂ on the surface of Mg-containing ironoxide film-coated iron powder was produced.

The composite soft magnetic powder of the present invention was chargedin moulds, and were press-molded into compacts, thereby a plate-shapedcompact having a dimension of length: 55 mm, width: 10 mm, andthickness: 5 mm, and ring-shaped compact having a dimension of externaldiameter: 35 mm, internal diameter: 25 mm, and height: 5 mm were formed.The obtained compacts were heat-treated under conditions of a nitrogenatmosphere, temperature: 500° C., and retention time: 30 minutes. Thus,composite soft magnetic materials constituted of a plate-shaped orring-shaped heat-treated article were produced. The composite softmagnetic material constituted of the plate-shaped heat-treated articlewas subjected to measurement of relative density, resistivity, andtransverse rupture strength, and the results are shown in Table.11.Winding was formed on the composite soft magnetic material constitutedof the ring-shaped heat-treated article, and magnetic flux density wasmeasured using a BH tracer. The result is shown in Table 11.

Conventional Example 13

Mg-containing ferrite-coated iron powder was prepared by formingMg-containing ferrite film on the surface of pure iron powder throughchemical process. Conventional mixed powder was produced by addingsilicone resin and MgO powder to the Mg-containing ferrite-coated ironpowder so as to have a mixing ratio of silicone resin:0.14, MgO:0.06,and the balance consisting of Mg-containing ferrite-coated iron powder.The obtained conventional mixed powder was charged in the moulds, andwas press-molded into compacts, thereby a plate-shaped compact having adimension of length: 55 mm, width: 10 mm, and thickness: 5 mm, andring-shaped compact having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of a nitrogen atmosphere,temperature: 500° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magnetic materialconstituted of the plate-shaped heat-treated article was subjected tomeasurement of relative density, resistivity, and transverse rupturestrength, and the results are shown in Table.11. Winding was formed onthe composite soft magnetic material constituted of the ring-shapedheat-treated article, and magnetic flux density was measured using a BHtracer. The result is shown in Table 11.

TABLE 11 Transverse Relative rupture Flux Constitution of Densitystrength density Resistivity Type soft magnetic powder (%) (MPa)B_(10KA/m) (μΩm) Composite soft magnetic Composite soft magnetic powder98 182 1.68 71 powder of the invention comprising: Mg-containing ironoxide film-coated iron powder particles that has iron powder particlesand Mg—Fe—O ternary-based oxide films which contain at least (Mg, Fe)Oand are coated on surfaces of the iron powder particles; and MgO—SiO₂composite oxide films which are composed of 2MgO•SiO₂ and are coated onsurfaces of the Mg-containing iron oxide film-coated iron powderparticles. Conventional composite Composite soft magnetic powder 98 1651.62 10 soft magnetic powder. comprising Mg-containing ferrite-coatediron powder particles which have Mg-containing ferrite layers formed bya chemical process, and surfaces of which are further coated withsilicone resin and MgO.

From the results shown in Table 11, it is understood that compared tothe composite soft magnetic materials made of the conventional compositesoft magnetic powder, composite soft magnetic materials produced usingthe composite soft magnetic powders of the present invention haveexcellent transverse rupture strength, magnetic flux density, andresistivity.

As stock powder, pure iron powder having mean grain size of 70 μm andcontaining trace amount of sulfur as unavoidable impurity was prepared.Oxidation-treated iron powder was produced by performing oxidationtreatment by retaining the pure iron powder at 220° C. for 2 hours inair. In addition, Mg powder having a mean grain size of 50 μm wasprepared. A mixed powder was produced by adding the prepared Mg powderto the oxidation-treated iron powder in a proportion ofoxidation-treated iron powder: Mg powder=99.8 mass %: 0.2 mass %, andmixing the powder. By heating the obtained mixed powder at a temperatureof 650° C. under a pressure of 1×10⁻⁴ MPa for 1 hour while tumbling themixed powder, Mg-containing iron oxide film-coated iron powder having acoating of deposition film on the surface of iron powder was produced.Thickness and maximum grain size of the deposition film formed on thesurface of the iron powder were determined by the observation of textureof a section of the deposition film using a transmission electronmicroscope. As a result, it was confirmed that the deposition film had athickness of 40 nm and maximum grain size of 20 nm.

The deposition film formed on the surface of Mg-containing oxidefilm-coated iron powder was analyzed using an X-ray photoelectronspectroscopic analyzer. Based on the analysis of bonding energies, itwas confirmed that fine metallic Fe particles were dispersed in thematrix of deposition film, and that outermost surface of the depositionfilm dispersing fine metallic Fe particles in its matrix was composed ofMgO. Concentration distributions of Mg, O, and Fe in depth direction ofthe deposition film were examined using an Auger electron spectroscopicanalyzer. As a result, it was confirmed that: the deposition film was aMg—Fe—O ternary-based oxide deposition film dispersing fine metallic Feparticles in its matrix; the Mg—Fe—O ternary-based oxide deposition filmhad concentration gradients where Mg and O decrease from the surfacetowards the interior direction, and Fe increases towards the interiordirection; and the outermost surface of the deposition film was composedof MgO. Sulfur distribution in boundary portion between the iron powderand the Mg—Fe—O ternary-based oxide deposition film was examined by amethod using an Auger electron spectroscopic analyzer. As a result, thepresence of a sulfur-enriched layer containing a higher concentration ofsulfur than that of the core portion of iron powder was confirmed in theboundary portion between the deposition film and the iron powder.

Prehydrosys alkoxysilane solution added with water and hydrochloric acidand magnesium-alkoxide solution were prepared. By mixing the solutionsin such a volumetric ratio that prehydrosys alkoxysilane solution:1magnesium-alkoxide solution:2, mixed oxide sol-solution of MgO and SiO₂was produced. The mixed oxide sol-solution of MgO and SiO₂ was added to,and mixed with the preliminary produced Mg-containing iron oxide-filmcoated iron powder, such that, in reduced mass of a mixture of MgO andSiO₂, 0.2 mass % was added in the mixed powder. By drying the mixedpowder by heating at a temperature of 150° C., composite soft magneticpowder of the present invention having coating of MgO—SiO₂ compositeoxide film composed of 2MgO.SiO₂ on the surface of Mg-containing ironoxide film-cpated iron powder was produced.

The composite soft magnetic powder of the present invention was chargedin moulds, and were press-molded into compacts, thereby a plate-shapedcompact having a dimension of length: 55 mm, width: 10 mm, andthickness: 5 mm, and ring-shaped compact having a dimension of externaldiameter: 35 mm, internal diameter: 25 mm, and height: 5 mm were formed.The obtained compacts were heat-treated under conditions of a nitrogenatmosphere, temperature: 500° C., and retention time: 30 minutes. Thus,composite soft magnetic materials constituted of a plate-shaped orring-shaped heat-treated article were produced. The composite softmagnetic material constituted of the plate-shaped heat-treated articlewas subjected to measurement of relative density, resistivity, andtransverse rupture strength, and the results are shown in Table.12.Winding was formed on the composite soft magnetic material constitutedof the ring-shaped heat-treated article, and magnetic flux density wasmeasured using a BH tracer. The result is shown in Table 12.

Conventional Example 14

Mg-containing ferrite-coated iron powder was prepared by formingMg-containing ferrite film on the surface of pure iron powder throughchemical process. Conventional mixed powder was produced by addingsilicone resin and MgO powder to the Mg-containing ferrite-coated ironpowder so as to have a mixing ration of silicone resin:0.14, MgO:0.06,and the balance consisting of Mg-containing ferrite-coated iron powder.The obtained conventional mixed powder was charged in the moulds, andwas press-molded into compacts, thereby a plate-shaped compact having adimension of length: 55 mm, width: 10 mm, and thickness: 5 mm, andring-shaped compact having a dimension of external diameter: 35 mm,internal diameter: 25 mm, and height: 5 mm were formed. The obtainedcompacts were heat-treated under conditions of a nitrogen atmosphere,temperature: 500° C., and retention time: 30 minutes. Thus, compositesoft magnetic materials constituted of a plate-shaped or ring-shapedheat-treated article were produced. The composite soft magnetic materialconstituted of the plate-shaped heat-treated article was subjected tomeasurement of relative density, resistivity, and transverse rupturestrength, and the results are shown in Table.12. Winding was formed onthe composite soft magnetic material constituted of the ring-shapedheat-treated article, and magnetic flux density was measured using a BHtracer. The result is shown in Table 12.

TABLE 12 Transverse Relative rupture Flux Constitution of Densitystrength density Resistivity Type soft magnetic powder (%) (MPa)B_(10KA/m) (μΩm) Composite soft magnetic Composite soft magnetic powder98 182 1.69 73 powder of the invention comprising Mg-containing ironoxide film-coated iron powder that has iron particles surface-coatedwith Mg—Fe—O ternary-based oxide films dispersing ultra-fine Fe grainsin its matrix, wherein surfaces of particles of the Mg-containing ironoxide film-coated iron powder are further coated with MgO—SiO₂ compositeoxide films composed of 2MgO—SiO₂. Conventional composite soft Compositesoft magnetic powder 98 165 1.62 10 magnetic powder. comprisingMg-containing ferrite-coated iron powder particles which haveMg-containing ferrite layers formed by a chemical process, whereinparticle surfaces of the Mg-containing ferrite-coated iron powder arecoated with silicone resin and MgO.

From the results shown in Table 12, it is understood that compared tothe composite soft magnetic materials made of the conventional compositesoft magnetic powder, composite soft magnetic materials produced usingthe composite soft magnetic powders of the present invention haveexcellent transverse rupture strength, magnetic flux density, andresistivity.

INDUSTRIAL APPLICABILITY

By producing composite soft magnetic materials using the Mg-containingoxide film-coated iron powder of the present invention, it is possibleto produce, stably, at low cost, composite soft magnetic materialshaving high resistivity, low eddy current loss, low coercive force, andlow hysteresis loss. Therefore, the present invention has an excellenteffect in terms of electric and electronic industries.

Where a composite soft magnetic materials is produced by press moldingMg-containing oxide film-coated iron powder of the present inventionhaving Mg—Fe—O ternary-based oxide deposition film dispersing extremelyfine metallic Fe particles in the matrix, the Mg—Fe—O ternary-basedoxide deposition film has high toughness by the presence of extremelyfine metallic Fe particles dispersed in the matrix, and is scarcelybroken down during the press molding of the Mg-containing oxidefilm-coated iron powder. Therefore, the obtained composite soft magneticmaterial has high resistivity, and low eddy current loss, low coerciveforce, and low hysteresis loss. In the present invention, it is possibleto produce composite soft magnetic materials having such properties.Therefore, the present invention has effective contribution to electricand electronic industries.

Where a composite soft magnetic material is produced by press moldingdeposition film-coated iron powder of the present invention, thedeposition film has high toughness by the presence of fine ironphosphide particles dispersed in the matrix, and is scarcely broken downduring the press molding of the deposition film-coated iron powder.Therefore, the obtained composite soft magnetic material has highresistivity, and low eddy current loss, low coercive force, and lowhysteresis loss. In the present invention, it is possible to producecomposite soft magnetic materials having such properties. Therefore, thepresent invention has effective contribution to electric and electronicindustries.

By producing composite soft magnetic materials using oxide depositionfilm-coated iron silicide powder of the present invention, it ispossible to produce, stably at low cost, composite soft magneticmaterials having high resistivity, and low eddy current loss, lowcoercive force, and low hysteresis loss. Therefore, the presentinvention has effective contribution to electric and electronicindustries.

By producing composite soft magnetic materials using oxide depositionfilm-coated iron-based Fe—Si-based powder of the present invention, itis possible to produce, stably at low cost, composite soft magneticmaterials having high resistivity, and low eddy current loss, lowcoercive force, and low hysteresis loss. Therefore, the presentinvention has effective contribution to electric and electronicindustries.

According to the present invention, it is possible to provide compositesift magnetic materials having high strength, high resistance, and highmagnetic flux density. Therefore, the present invention has effectivecontribution to electric and electronic industries.

The invention claimed is:
 1. A Mg-containing oxide film-coated ironpowder comprising: metallic iron powder particles; and Mg—Fe—Oternary-based oxide deposition films which contain at least (Mg,Fe)O andcoat the surfaces of the metallic iron powder particles, wherein the(Mg,Fe)O is a crystalline MgO-dissolving wustite phase, and each of theMg—Fe—O ternary-based oxide deposition films has a concentrationgradient of Mg, Fe and O.
 2. A Mg-containing oxide film-coated ironpowder according to claim 1, further comprising sulfur-enriched layersin boundary portions between the iron powder particles and the Mg—Fe—Oternary-based oxide deposition films at least containing (Mg,Fe)O,wherein sulfur concentrations of the sulfur-enriched layers are higherthan that of sulfur contained as an unavoidable impurity in centralportions of the iron powder particles.
 3. A Mg-containing oxidefilm-coated iron powder according to claim 1, wherein the Mg—Fe—Oternary-based oxide deposition films at least containing (Mg,Fe)O havemicrocrystalline structures having a grain size of 200 nm or less.
 4. AMg-containing oxide film-coated iron powder according to claim 1,wherein outermost surfaces of the Mg—Fe—O ternary-based oxide depositionfilms at least containing (Mg,Fe)O have uppermost portions that aresubstantially composed of MgO.
 5. The Mg-containing oxide film-coatediron powder according to claim 1, wherein the concentration gradient issuch that Mg and O increase towards an upper surface of the Mg—Fe—Oternary-based oxide deposition film, while Fe decreases towards saidsurface.
 6. The Mg-containing oxide film-coated iron powder according toclaim 1, wherein the Mg—Fe—O ternary-based oxide deposition films areformed through first and second oxidization treatments on the metalliciron powder particles.
 7. A composite soft magnetic material that hasbeen produced using a Mg-containing oxide film-coated iron powderaccording to claim 1, comprising an iron particle phase and grainboundary phase surrounding the iron particle phase, wherein the grainboundary phase contains Mg—Fe—O ternary-based oxide which includes acrystalline MgO-dissolving wustite phase.
 8. A composite soft magneticmaterial according to claim 7, wherein a magnetic flux density of thecomposite soft magnetic material is 1.66 to 1.69 T.
 9. Anelectromagnetic circuit component comprising a soft magnetic materialaccording to claim
 6. 10. An electromagnetic circuit component accordingto claim 9, wherein the electromagnetic circuit component is a magnetcore, core of a motor, core of a generator, solenoid core, ignitioncore, reactor, transformer, choke coil core, or magnetic sensor core.11. An electric device equipped with an electromagnetic circuitcomponent according to claim 9.